KR101097660B1 - XML Query Processing Method On Wireless Broadcasting Stream - Google Patents

Abstract

The present invention relates to a method for processing XML queries, and more particularly, to minimize the size of a broadcast stream through structural summaries and attribute summaries, and to inter-node nodes using PC bitstrings and packing information. The present invention relates to a method for processing XML queries in a wireless broadcast stream by supporting branch query processing in a wireless broadcasting environment by maintaining a parent-child relationship, and selectively receiving attributes and texts.

As described above, the present invention significantly shortens the access time and tuning time in processing various types of queries including branch queries, and thus has excellent energy efficiency.

XML, Broadcast Stream, Property Summary, Index, Data, Tree, Branch Query

Description

XML Query Processing Method On Wireless Broadcasting Stream

The present invention relates to a method for processing XML queries, and more particularly, to minimize the size of a broadcast stream through structural summaries and attribute summaries, and to inter-node nodes using PC bitstrings and packing information. The present invention relates to a method for processing XML queries in a wireless broadcast stream by supporting branch query processing in a wireless broadcasting environment by maintaining a parent-child relationship, and selectively receiving attributes and texts.

BACKGROUND With the development of wireless communication technology, wireless mobile computing technology that transmits and receives data through portable terminals (laptops, PDAs, mobile phones, etc.) is spreading. In a wireless mobile environment, data transmission via wireless broadcasting is an effective way to provide the benefits of bandwidth utilization, energy efficiency and scalability.

In a wireless broadcast environment, the server continues to broadcast data over the broadcast channel, and mobile users receive the necessary data from the broadcast channel. The server sends data in a broadcast manner, so it can efficiently utilize a limited network bandwidth and does not incur additional costs even if the number of mobile users increases. In addition, the mobile user has the advantage of being able to access the data by only "receiving" without energy-consuming "transmission" operation.

In a wireless broadcasting environment, mobile users use portable terminals with limited battery resources, so that selective reception of data is required for energy saving. Through selective reception, the mobile user can efficiently use energy by receiving data in the active mode and waiting until the broadcast time of the required data in the doze mode when the required data is not broadcast. In addition, the overall query processing time should be minimized to provide fast response to mobile users.

Generally, the former is referred to as energy efficiency and the latter as access time efficiency. In order to measure the energy efficiency and access time efficiency of mobile users in data transmission through broadcasting techniques, tuning time and access time are used as measures of performance measurement, respectively.

The access time means the time required from the start of the mobile user's query to the time when all necessary data is received, and the tuning time means the sum of the times that the mobile user actually reads data from the broadcast channel.

In general, XML (eXtensible Markup Language) is widely used as a standard for information presentation and exchange in a wireless broadcasting environment. Accordingly, efficient query processing has emerged as an important issue in XML documents.

An XML document is a semi-structured language in which elements are hierarchically nested and can be represented as an ordered, labeled tree starting from the root. In an XML document, elements, attributes, and text may be represented as nodes in a tree, and parent-child relationships may be represented as edges between nodes.

1A illustrates a conventional XML document. The XML document as shown in FIG. 1A may be represented in a tree form as shown in FIG. 1B.

Nodes represented by ellipses that are solid lines in FIG. 1B represent elements of the XML document, and the edges between the nodes represent parent-child relationships. The number contained in the ellipse indicates the Dewey order of each node. The Dewey order in an XML document is a vector representing the path from the root of the document to its nodes, with each node having a unique Dewey order. Attributes and texts are omitted for ease of explanation.

Query expressions for XML documents, on the other hand, use a path expression query language such as XPath or XQuery. For example, the query "Search for a city in Czech Republic" in the XML document of FIG. 1A may be expressed as follows using an XPath path expression query.

XPath query processing consists of a search of a location path, and a search of the location path consists of the processing of each of the location steps that make up the query, and the processing of the location step involves each term in the query. This means checking the corresponding axis, node or conditional expression.

For example, the query consists of four location steps (ie modial, / country [@name = "Czech Republic"], / province, / city). Thus, the first position step process looks for a "modial" node that is the root, and the second position step process looks for a "country" node whose "name" attribute value is "Czech Republic" among the child nodes of the "modial" node. The third position step process is to search for the "province" node among the children of the "country" node satisfying the second position step, and the last position step is to search for the "city" node which is the end node of the query.

Hereinafter, the branch query will be briefly described. A Twig Query is a query expression that finds a pattern that simultaneously satisfies a conditional expression for several elements in a tree structure XML data.

The branch query consists of two or more parent-child relationships, ancestor-descent relationships, including conditional expressions for element tags, attributes, or text. For example, in the example document of FIG. 1A, a branch query for searching for a city located in a province where a country is named may be expressed as follows.

Similarly, a query for searching for a city in "Liege" among provinces with the name of a country is expressed as follows:

FIG. 2 illustrates the aforementioned branch query in a tree form, and the edges and nodes indicated by dotted lines in FIG. 2 denote attributes.

Branch query is a widely used query type because of its ability to contain complex content. It is a key part of XML query processing.

Although many researches have been conducted on XML branch query processing and wireless XML broadcasting techniques, the XML branch query processing techniques proposed so far do not consider energy and access time efficiency, which are important measures in wireless mobile computing environment. Since studies on wireless XML broadcasting only consider simple path queries without branch conditions, branch query processing is not possible or inefficient.

Meanwhile, in XML query processing, structural summaries and related techniques are used to effectively reduce the size of index information by grouping elements with the same path. However, this structural summary method has a great effect on reducing access time in a wireless broadcasting environment, but because it does not preserve the order of elements, it cannot process queries containing conditional expressions and the parent-child relationship between elements disappears. Therefore, there is a problem in that the branch query cannot be processed because the query including the conditional expression cannot be processed and the parent-child relationship between elements is lost.

In order to solve the above problems, an object of the present invention is to minimize the size of a broadcast stream through structural summaries and attribute summaries for processing energy and access time efficient XML branch queries in a wireless broadcasting environment. Wireless broadcast streams that support branch query processing by inserting PC bit streams and compressed information to maintain parent-child relationships, and provide selective indexing of attributes and text, minimizing access and tuning times for mobile users Provides a way to process XML queries.

The XML query processing method in the wireless broadcast stream according to the present invention can be summarized as the following features.

○ Structure summary and property summary

The size of the broadcast stream is minimized by omitting duplicate tag names and attribute names.

○ Optional reception of attribute values and text

The energy efficiency of mobile users can be improved by selectively receiving only attribute values or text included in the conditional expression given in the query. In particular, by overriding the attribute values and the text with the Dewey order, we overcome the limitations of the structured summary method, which was impossible to process queries with conditional expressions.

○ Parent-Child Relationship Maintenance Techniques for Branch Query Processing

In the present invention, branch query processing is supported by maintaining a parent-child relationship through a P-C bitstring and packing information.

Intuitive query processing using query tree

By creating a query tree for a given query, we provide a stream reception and intuitive query processing method according to the query processing steps in the query tree.

The XML query processing method through the problem solving means of the present invention as described above generates a group node through the structural summary and the attribute summary, and the PC bitstring (PC Bitstring) and compression information for representing the parent-child relationship to the group node Generating a broadcast stream including (Packing Information) and analyzing the query to generate a query tree, and selectively receiving the broadcast stream and processing the query.

Here, the attribute summary may reduce the size of the broadcast stream by omitting duplicate tag names and attribute names in the broadcast stream and storing only the attribute value and order information of elements having the attribute value.

The group node may include a group name, a location path, a child node address, a PC bitstring, packing information, and an attribute name list. It includes an index including text addresses, data including an attribute value list and a text list.

Herein, the child node address is address information of child group nodes of the group node, and the PC bit string indicates whether or not there is a child element of an element of a parent group node of the group node. The compressed information is information representing the number of child elements belonging to one parent element, and the attribute name list includes the name of the attribute and the start address of the stream in which the attribute values are continuously stored. The text address is a start address of a stream in which texts of an element belonging to the group node are continuously stored, and the attribute value list is a list in which attribute values and Dewey order of elements merged in the group node are sequentially stored for each attribute name. And the text list is merged into the group node A list of the stored texts are grouped together and Dewey Order of the tree.

In addition, the processing of the query may include generating a query tree and receiving an index of the group node when the query is a simple path query that does not include a branch condition to find a group node of a next position in the child address. Searching the query tree from the top to the bottom, and searching up to the last node of the query tree and returning information of the group node corresponding to the last node of the query tree as a result of the query.

The searching of the query tree may include: when the user's query includes a condition expression, the name of the attribute included in the attribute name list among the attribute summary group nodes and the start address information of the stream in which the attribute values are continuously stored. By selectively receiving only the attribute value or text included in the given conditional expression, and storing the Dewey order satisfying the conditional expression in the query tree.

Here, when there is a Dewey order stored by the conditional expression in the query tree, only the information corresponding to the Dewey order is returned as a result of the query.

The processing of the query may include generating a query tree and searching a path to the query tree when the query includes a branch condition, and whether or not the PC bit string matches to select elements satisfying the branch condition. And determining the query result by applying the selected PC bit string to an end group node.

The searching of the path may include searching for a main path, which is a path including data to be searched, and searching for a sub path including a given branch condition, and searching for the group nodes corresponding to the main path and the sub path. And receives and stores the PC bit string and the compressed information in each node of the query tree.

The determining whether the PC bit string matches may include selecting an element satisfying the branch condition using the PC bit string and the compression information stored in each node of the query tree through searching the path, wherein the query tree is selected. In the step of going up from the end node of the main path and the sub-path to the branch node to perform a bit-wise AND operation by compressing the PC bit string according to the compression information, the branch node of the query tree is calculated from the main path and the sub-path The intermediate result value satisfying the branch condition is calculated by bit-wise ANDing the bit string.

The deriving of the query result may include restoring the intermediate result value calculated at the branch node to the original bit string while descending along the main path in the query tree, and the bit string restored to the full node of the main path is an end group. Applied to the data of the node, only the content of the element corresponding to 1 in the bit string is returned as a query result.

The present invention relates to a method for efficiently reducing XML access and branching time, which is an important measure in a wireless broadcasting environment. In addition, the selective reception of attribute values and text results in an excellent effect that effectively reduces tuning time.

In addition, the present invention overcomes the limitation of processing a query including a conditional expression in a query processing method using a structured summary in a wireless broadcasting environment by storing attribute values and texts together with a Dewey order, and using a PC bit string and compressed information. By maintaining the parent-child relationship, there is an excellent effect of supporting efficient branch query processing.

In addition, the present invention supports an intuitive and efficient branch query processing method for a mobile user by generating a query tree corresponding to a given query and selectively receiving a broadcast stream according to the query processing step. That is, the mobile user receives the group node of the stream corresponding to the location step of each processing in the query tree, stores the PC bit string and compression information, which are index information for branch query processing, and performs a bit-wise operation in the query tree. By selecting the information of the element satisfying the branch condition, the mobile user first receives the index including the index information in the XML stream, and then selects the information only when the conditional expression for the attribute or the text is given in the query tree. In this case, an excellent effect of securing energy efficiency occurs.

Hereinafter, specific embodiments of the present invention will be described in detail with reference to the drawings.

The present invention relates to an XML query processing method, comprising a server end for generating and transmitting a wireless broadcast stream and a client end of a mobile user receiving the broadcast stream to perform XML query processing.

That is, in the XML query processing method according to the present invention, a client end (terminal) of a mobile user receives a broadcast stream generated by a server-side broadcast stream generating apparatus or program, and a processor of the client end receives a broadcast stream for the received broadcast stream. Perform query processing.

As described above, the generation of a broadcast stream according to the present invention is performed by a broadcast stream generation device or a generation program at the server side, and the query processing will be described on the premise that the processor at the client side performs it.

Hereinafter, the structural features of the present invention will be described in detail, and then a detailed XML query processing method will be described.

<XML Broadcast Stream Structure for Wireless Broadcasting>

The present invention has a structure of a group node in which elements having the same path are merged using structural summaries in an XML broadcast stream, and features an attribute summarization and a selective reception method according to attributes.

Group Node Structure

The present invention generates a broadcast stream of an XML document as a broadcast stream of a group node by merging elements having the same path into one node to generate one group node.

The group node according to the present invention can be represented as follows.

GN _P = [I _P , D _P ], where GN _P is a group node that merges all elements (e _P ) whose path is P in the original XML document, where I _P and D _P are the indexes of the group nodes, respectively. ) And data.

The I _P is a tag name (tn _e ), a location path IP _e , a child address, a PC bitstring, packing information, and a list of attribute names of e _P merged with GN _P ( It may be configured to include an attribute name list and a text address.

Herein, the child address is address information of child group nodes, the PC bit string and compression information are information representing parent-child relationships of elements merged into a group node, and the attribute name list is a name of an attribute and the The values of the attribute include the start address information of the stream in which the values are continuously stored, and the text address is the start address of the stream in which the texts of the elements belonging to the group node are continuously stored.

The DP may include an attribute value list and a text list.

Here, the attribute value list is a list in which the attribute values and the Dewey order of the elements merged in the group node are sequentially stored for each attribute name. to be.

FIG. 3 schematically illustrates the structure of a group node according to a preferred embodiment of the present invention. In the example of the XML document of FIG. 1A, the structure of the group node whose path is "/ mondial / country / province" is shown.

Referring to FIG. 3, an index (Index, I _P ) of a group node is a collection of index information for a mobile user to selectively receive an XML stream, which is an essential part of receiving a group node in a broadcast channel.

The index is a tag name (group name) of the group node "province", a location path "/ modial / country / province.", An address for the "city" group node as a child address, a bit string 1111, a PC bit string, Compressed information string 2.1.1, the stream start address of the "id" attribute and the "name" attribute value of the "province" elements, the attribute name list, and the stream start of the text of the "province" elements, the text address. It consists of an address.

Here, the address included in each index information means time information when the corresponding data is broadcast in the XML data stream. The name and path of the group node is used to identify the group node, and the child address is used for selective reception of the "city" group node in the broadcast stream.

The attribute name list and the text address are used to selectively receive only the attribute value or text included in the conditional expression among the data.

The PC bit string is information representing whether or not an element of the group node exists as a child element of an element of a parent group node as a continuous bit string of 0 or 1, and the compressed information is the number of child elements belonging to one parent element. Information that indicates.

In addition, the data DP includes a list of attribute values in which the values of the "id" attribute and the "name" attribute are sequentially stored with the Dewey order. Here, since the "province" elements have no text, nothing is stored in the text list. (Null)

The group node merges several elements of the same path into one node, but stores the attribute value and text of each element with the order of the elements of the element to maintain the element order information in the original XML document. Can be processed.

 -Property summary

The present invention summarizes the attributes of the group nodes and optionally receives the summarized attributes and texts to minimize the size of the stream and shorten the tuning time of the mobile user.

In XML, an attribute consists of a pair of attribute names and attribute values, and an element can have multiple attributes. In this case, elements with the same path and tag name generally have a structural characteristic using the same attribute name.

For example, in the XML document of FIG. 1A, the "province" elements have a common attribute of "id" and "name". Therefore, if the same attribute name is repeated several times, the repeated attribute name is omitted and only the attribute value and the order information of the element having the attribute value are stored, thereby minimizing and moving the stream size while maintaining the order of elements in the original XML document. User's tuning time can be shortened.

The attribute summary method according to the present invention omits duplicate attribute names as described above, and stores the attribute values and the Dewey order of elements having the values to efficiently process a query including a conditional expression for the attributes. Indexing method.

FIG. 4 illustrates a simplified example of attributes of the "province" node in the example XML document of FIG. 1A using an attribute summary method.

As can be seen from FIG. 4, the size of the stream can be effectively reduced by omitting all duplicate attribute names through the attribute summary method according to the present invention.

On the other hand, the attribute name is stored in the attribute name list together with the start address in the stream in which the attribute value is continuously stored, and the attribute values of the same name are successively added to the attribute value list of the group node with their respective Dewey order. Stored.

Since text and attributes, which are strings, account for the majority of the entire stream compared to index information in XML documents, the structured summary omits the tags of elements with the same path and separates attribute names and values. Receiving only attribute values reduces access time and tuning time.

5 is a diagram for an example of selectively receiving using an attribute summary method for a query including a conditional expression according to a preferred embodiment of the present invention.

5 is a case where the conditional expression is "/ mondial / country / province [@ id =" f0_17473 "]". Referring to FIG. 5, since the attribute name list includes a start address of a portion in which "id" and "name" attribute values are stored consecutively, the client-side processor of the mobile user may determine the entire attribute of the "province" elements. By selectively receiving and searching only the attribute values corresponding to the attribute name "id" without searching, the query including the conditional expression can be efficiently processed.

<P-C Bitstring and Packing Information for Processing Branching>

In the conventional method using the structural summary, since the information of the parent-child relationship is not maintained, there is a problem that an accurate result cannot be returned when processing a branch query.

In the present invention, in order to solve the problem of returning an incorrect result set due to the absence of information of a parent-child relationship, the P-C bit string and compression information are used.

6 shows the result of processing a query (// country [name] / province) for a province located in a country whose country is specified in a tree (a) of the original XML document and a tree (b) using a structured summary. It is shown.

As shown in (a) of FIG. 6, in the original XML document, only the “province” nodes 4 and 7 which are children of the “country” node 2 satisfying the branching condition are accurate results.

However, the method using structured summarization does not maintain the parent-child relationship of the elements, so branch queries cannot be processed because it is not possible to identify which of the merged "province" elements is a child of the "country" element twice. .

In the present invention, the parent-child relationship is represented through the P-C bit string and the compressed information, so that the exact result is returned during the branch query processing. The P-C bit string indicates whether or not an element of the corresponding group node exists among child elements of an element belonging to a parent group node.

That is, if an element belonging to the corresponding group node exists among the children of an element belonging to a parent group node, it is represented by 1; Using bits to represent parent-child relationships provides the following advantages:

By expressing the parent-child relationship using small bits, the index information can be reduced in weight and stream size. Bit-Wise operation enables intuitive and fast operation.

On the other hand, in XML, when one element can have several elements with the same name as children, when the parent-child relationship is expressed in a P-C bit string, the child elements corresponding to each parent element cannot be distinguished correctly.

In the present invention, compressed information is used to distinguish child elements corresponding to each parent element. The compressed information is information indicating the number of elements having the same parent among the elements belonging to the group node. Each number in the compressed information corresponds to each element belonging to the parent group node in order.

7 illustrates P-C bit strings and compression information of a group node generated through structural summaries from an example XML document according to a preferred embodiment of the present invention.

For example, the PC bit string 100 of the "name" group node 3 indicates that only the first "country" element among the elements belonging to the "country" group node which is the parent group node has the "name" element as its child. it means.

The compressed information 1.1.1 means that the bits of the P-C bit string correspond to one parent element, respectively. Similarly, the P-C bit string 1111 of the "province" group node 4 means that there are a total of four "province" elements among the child elements of elements belonging to the "country" group node which is the parent group node.

Compressed information (2.1.1) means that the first and second "province" elements have the same parent, and the parent elements corresponding to the third and fourth bits are different.

<Query processing method in XML broadcast stream>

Hereinafter, a query processing method using a broadcast stream will be described. Query processing in XML broadcast stream can be divided into general path expression query without branch condition and branch query with branch condition. Given a query, the mobile user analyzes the query, creates a query tree, and traverses the query tree from the top down. Therefore, after briefly describing the query tree generation, the query processing method will be described in detail.

When a query is given, the processor of the mobile terminal owned by the mobile user analyzes the query, generates a query tree for efficient query processing, and selectively receives a stream according to each step to perform the query processing.

Each node of the query tree corresponds to a location step in a location path, and the user receives a group node corresponding to each node of the query tree while searching the query tree from the top down.

8 shows examples of various query trees for different queries.

Internal nodes except leaf nodes in the query tree receive only the index of the group node to search for the node corresponding to the next location step if no attribute or text expression is given. When the conditional expression is given to the intermediate node, the mobile user selectively receives only the attribute value or text data corresponding to the conditional expression among the data of the group node by using the index information included in the index.

Simple path query processing

First, the simple path query processing without the branch condition will be described.

Given a query, the processor of the mobile terminal possesses a query tree to search the query tree from the top node down.

The search of the query tree consists of receiving the index of the group node and finding the group node of the next position level in the child addresses.

At this time, if the positional step of the query tree includes a conditional expression for an attribute or text, the attribute value corresponding to the conditional expression among the data of the group node using the attribute name list or text address of the index It selectively receives only text and stores the Dewey order that satisfies the conditional expression in the query tree.

After searching to the last node of the query tree, the information of group node corresponding to the last node of the query tree is returned as the query result. If there is a Dewey order stored by the conditional expression in the query tree, only the information corresponding to this Dewey order is returned as the query result.

9 is a query tree search process (a) for a simple path query (/ mondial / country / province [@ name = "Aland" / city / text ()) including a conditional expression for an attribute according to an exemplary embodiment of the present invention. And (b) the optional reception of an XML data stream.

Given a query, the mobile user creates a query tree as shown in FIG. 9 (a) and searches the query tree from the top down.

First, the "mondial" group node, which is the root of the group node tree, is received and searched for and received from the child addresses of the "country" group node corresponding to the next step of the query tree.

In the same way, after receiving the "country" group node, the next step in the query tree is searched for the address of the "province" group node. After receiving the " province " group node, it searches for and receives the start address where the values of the " name " attribute are stored in the index's attribute name list to process the conditional expression given in this position step.

The attribute value in the attribute value list of the "province" group node is searched for the Dewey order (1.3.1) of the "Aland" element and stored in the "province" node of the query tree.

Finally, we receive the "city" group node, the end node of the query tree, and selectively receive only the portion of the text address where the text is stored. As a result of this query, only text data (Mariehamn) corresponding to the descendants of the Dewey order (1.3.1.1) stored in the query tree is returned as the result.

Branch Query Processing

Next, the query processing method will be described when a branch condition is given.

Given a branch condition, query processing includes a path traversal phase for the query tree, a PC bit string matching phase to select elements that satisfy the branch condition, and a selected PC bit. It involves the application of heat to the end group nodes to produce a result (retrieval phase).

The path traversal phase for the query tree is composed of a main path traversal and a sub path traversal, where a main path is a path including data to be found. And a sub path is a path including a given branch condition.

For example, in a query that retrieves the name of a city with population information (/ mondial / country / city [population] / name), the primary path is the path that contains the name of the city, which is the data you want to find (/ mondial / country / city / name), and the secondary path is the path (/ mondial / country / city / population) that contains the population information given in the quarter condition. There can be multiple secondary paths depending on the branching conditions given in the query.

In the path traversal phase, a group node corresponding to a primary path and a secondary path is received in an XML stream, and the P-C bit string and compressed information are stored in each node of the query tree.

In the P-C bit string matching phase, an element satisfying the branch condition is selected using the P-C bit string and the compressed information stored in each node of the query tree through the path traversal phase.

In this process, bit-wise AND operations are performed by packing the P-C bit string according to the compression information while going up from the end node to the branch node of the main path and the sub path in the query tree.

In the branch node of the query tree, a bit-wise AND operation is performed on the bit strings computed on the main path and the sub path to calculate an intermediate result value satisfying the branch condition.

Finally, in the retrieval phase, the PC bit string is applied to an end group node to obtain a result. The intermediate result value calculated at the branch node is unpacked to the original bit string while descending along the main path in the query tree. do.

The bit string restored to the end node of the main path is applied to the data of the end group node, and only the content of the element corresponding to 1 in the bit string is returned as a result.

10 shows an example of processing another branch query (/ mondial / country [name] / province / city) in the preferred embodiment of the present invention.

The processor of the mobile terminal possesses the query tree from the given query and searches for the primary path (/ mondial / country / province / city) and the secondary path (/ mondial / country / name).

Receive the "mondial" group node, the root of the query tree, and receive the "country" group node, the next step in the query tree, from the child addresses.

After receiving the "country" group node that branches in the query tree, the child nodes of this group node are used to group the node nodes in the order in which they are first broadcast, from the group node on the primary route and the group node on the secondary route. Receive.

First, it receives the "name" group node and stores the P-C bit string and the compressed information. Next, it receives the "province" group node and stores the P-C bit string and the compressed information in the query tree.

Finally, we receive the "city" group node, which is the end node of the main route, from the child addresses of the "province" group node.

After the path traversal phase for the query tree is completed, the P-C bit string matching phase is performed from the end node to the branch node of the main path and the sub path.

First, the P-C bit string 111111 of the "city" group node, which is an end node of the main path, and the P-C bit string 1111 of the "province" group node, which is the parent node, are bit-wise ANDed.

At this time, the P-C bit string of the "city" group node is compressed to 1111 by compression information (2.1.2.1). That is, in the original P-C bit string, the first, second, fourth and fifth bits are OR-ing and compressed into one bit because their parents are the same.

Similarly, the result 1111 calculated up to the "province" group node and the P-C bit string 111 of the "country" group node which is the parent group node are bit-wise ANDed to calculate the intermediate result 111 of the main path.

In the same manner, the intermediate result 100 of the sub path is calculated by bit-wise ANDing the P-C bit string from the "name" group node, which is the end node of the sub path, to the "country" group node, which is the branch node.

A bit string 100 that satisfies the branching condition is calculated by bit-wise ANDing an intermediate result between the main path and the sub-path at the branch node.

The bit string calculated at the branch node is restored along the main path to the original bit string using the P-C bit string and the compressed information stored in each node. Since the compressed information of the "province" node is (2.1.1), the intermediate result 100 is restored to 11, the bit string before the first 1 is compressed, and the intermediate result is 1100.

Next, since the compressed information of the "city" node is (2.1.2.1), the first and third bits are restored to 11 and 00 at 1100, respectively. Therefore, since the final bit string for the query terminal group node "city" is 111000, elements satisfying the branch query are the first to third elements among the elements merged into the "city" group node.

Therefore, only the "city" elements of the 5th, 6th and 8th are returned as the result of this query.

In order to measure the performance of the query processing method according to the present invention as described above, a simple path query and a branch query were evaluated on an actual data set.

Performance comparison is based on the method of streaming and broadcasting to one node (hereinafter, S-node) and the access time and tuning time of the method of simplifying and broadcasting data of elements having the same path to one node (hereinafter, path-summary). Was evaluated.

However, since the path summary does not support a query including a conditional expression or a branch query, only the simple path query was experimented.

In this experiment, we generated XML stream for wireless broadcasting using mondial XML document which is a real data set and measured access time and tuning time for query processing.

To measure performance, we use the standard language query, XPath query, which uses four simple path queries without condition expressions, simple path queries with conditional expressions, branch queries without conditional expressions, and branch queries with conditional expressions. The type of query was evaluated.

Table 1 below describes the data sets and queries used in the experiment.

S1 and S2 are queries for measuring simple path queries. Simple path queries with conditional expressions were measured using SP1 and SP2. T1 and T2 are branch queries that do not include conditional expressions. Branch queries containing conditional expressions were measured using TP1 and TP2.

Figure 11 compares the size of the original XML document, Path Summary, SL, SD, SP, and XML stream generated according to the present invention. The SL, SD, and SP methods are known methods proposed by S-node.

As shown in the experimental results, the path summary, the SL, the SD, the SP, and the XML stream generated according to the present invention reduced the size of the original XML document by 52.9%, 38.6%, 33.5%, 33.5%, and 42.4%, respectively.

The data set used in the experiment is small in size and has a large number of elements that do not contain attributes. Therefore, in the XML stream generated according to the present invention, the stream reduction efficiency due to the attribute summary is lower than that of the stream due to the added index information such as PC bitstring and packing information. The size of the generated XML stream was smaller than that of the original XML document or the S-node, but was larger than the XML stream generated by the Path Summary. However, if the number of elements including the attribute is large, such as the actual broadcast stream environment, it is certain that the size will be smaller than the XML stream generated by the path summary.

12 shows the result of measuring the access time.

In this experiment, since the path summary method only supports simple query processing, we did not measure the performance of SP1 ~ TP2. The present invention showed better performance on average than other methods, and the access time of 73.4%, 66.9%, 63.3%, and 30.8% was shortened compared to the SL, SD, SP, and Path Summary methods, respectively.

In particular, in the query measurement results for S2 ~ TP1 queries, the performance of the proposed method is significantly improved compared to S-node, which searches for nodes scattered throughout the stream because S-nodes form streams in the order of the elements in the XML document. On the other hand, the proposed method terminates the query processing early because the structure is summarized and merged into one group node.

However, in the access time measurement for S1 query, the path summary method with the smallest stream showed the best performance because the result value of the query is located in the latter part of the XML document used in the experiment. It was proportional to the size of.

13 shows the results of measuring tuning time.

As with the access time measurement, the tuning time of the Path Summary method was measured only for the S1 and S2 queries. As can be seen from the experimental results, the present invention showed better performance in tuning time performance measurement than access time in comparison with other methods. The present invention reduced the access time of 95.5%, 90.4%, 75.4%, and 40.7%, respectively, compared to the SL, SD, SP, and Path Summary methods.

This is explained for the following reasons.

1) In the present invention, after receiving only the index part by separating the index and the data, and selectively receiving the attribute values or the text given in the condition, tuning is performed when the condition is included in the query or when there is no text at the end node of the query. The time is effectively reduced.

2) Especially in the case of branch queries, the tuning time is greatly increased because the S-node receives more nodes than the simple path query to select the result that satisfies the branch condition. However, in the proposed method, the tuning time is increased. Because PC bitstring and packing information are used to select elements that satisfy branch conditions, it showed excellent performance in branch query processing.

While the present invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention.

FIG. 1A illustrates a conventional XML document, and FIG. 1B illustrates a representation of the XML document of FIG. 1A in a tree form.

2 is a representation of such a branch query in the form of a tree.

FIG. 3 schematically illustrates the structure of a group node according to a preferred embodiment of the present invention. In the example of the XML document of FIG. 1A, the structure of the group node whose path is "/ mondial / country / province" is shown.

FIG. 4 illustrates a simplified example of attributes of the "province" node in the example XML document of FIG. 1A using an attribute summary method.

5 is a diagram for an example of selectively receiving using an attribute summary method for a query including a conditional expression according to a preferred embodiment of the present invention.

6 shows the result of processing a query (// country [name] / province) for a province located in a country whose country is specified in a tree (a) of the original XML document and a tree (b) using a structured summary. It is shown.

7 illustrates P-C bit strings and compression information of a group node generated through structural summaries from an example XML document according to a preferred embodiment of the present invention.

8 shows examples of various query trees for different queries.

9 is a query tree search process (a) for a simple path query (/ mondial / country / province [@ name = "Aland" / city / text ()) including a conditional expression for an attribute according to an exemplary embodiment of the present invention. And (b) the optional reception of an XML data stream.

10 shows an example of processing another branch query (/ mondial / country [name] / province / city) in the preferred embodiment of the present invention.

Figure 11 compares the size of the original XML document, Path Summary, SL, SD, SP, and XML stream generated according to the present invention.

12 shows the result of measuring the access time.

13 shows the results of measuring tuning time.

Claims (10)

Generating a group node through the structural summary and the attribute summary, and generating a broadcast stream including a P-C bitstring and packing information representing a parent-child relationship to the group node; Analyzing a query to generate a query tree and selectively receiving the broadcast stream and processing the query if a query is given, The group node is Group name, Location path, Child node address, PC Bitstring, Packing information, Attribute name list, Text address an index including addresses); An XML query processing method in a wireless broadcast stream comprising data including an attribute value list and a text list. Herein, the child node address is address information of child group nodes of the group node, and the PC bit string indicates whether or not there is a child element of an element of a parent group node of the group node. The compressed information is information representing the number of child elements belonging to one parent element, and the attribute name list includes the name of the attribute and the start address of the stream in which the attribute values are continuously stored. The text address is a start address of a stream in which texts of an element belonging to the group node are continuously stored, and the attribute value list is a list in which attribute values and Dewey order of elements merged in the group node are sequentially stored for each attribute name. And the text list is merged into the group node A list of the stored texts are grouped together and Dewey Order of the tree. The method of claim 1, The attribute summary above The method of claim 1, wherein the size of the broadcast stream is reduced by omitting duplicate tag names and attribute names in the broadcast stream and storing only attribute values and order information of elements having the attribute values. delete The method of claim 1, Processing the query When the query is a simple path query without a branch condition Searching the query tree from the top node down from the top node by generating a query tree and receiving an index of the group node to find a group node at a next position in the child address; And searching for the last node of the query tree and returning information of the group node corresponding to the last node of the query tree as a result of the query. The method of claim 4, wherein Searching the query tree Your query contains conditional expressions Satisfies the conditional expression by selectively receiving only the attribute value or text included in the given conditional expression through the start address information of the stream in which the attribute name and the value of the attribute are sequentially stored among the attribute summary group nodes. And storing the Dewey order in a query tree. The method of claim 5, If the query tree has a Dewey order stored by a conditional expression And processing only the information corresponding to the Dewey order as a result of the query. The method of claim 1, Processing the query If the query includes a branch condition Creating a query tree and searching for a path to the query tree; Checking whether a P-C bit string matches to select elements satisfying the branch condition; And applying the selected P-C bit string to an end group node to derive a query result. The method of claim 7, wherein Searching for the route A search for a main path that is a path that contains the data to find and a search for a sub-path containing a given branch condition; And receiving the group nodes corresponding to the primary path and the secondary path, and storing P-C bit strings and compression information in each node of the query tree. The method of claim 8, Checking whether the P-C bit string matches Searching for the path to select elements satisfying the branching condition using P-C bit strings and compression information stored in each node of the query tree; In the query tree, a bit-wise AND operation is performed by compressing a PC bit string according to compression information while going from an end node of a main path and a sub path to a branch node, and in the branch node of the query tree, the main path and sub paths. And performing a bit-wise AND operation on the bit string computed in step 2 to calculate an intermediate result value that satisfies a branch condition. The method of claim 9, Deriving the query result The intermediate result value calculated at the branch node is restored to the original bit string while descending along the main path in the query tree, and the bit string restored up to the full node of the main path is applied to the data of the end group node so that Method for processing XML query in wireless broadcast stream, characterized in that only the content of element corresponding to 1 is returned as query result.

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