JP3601416B2 - Information retrieval method and device - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an information search method and apparatus suitable for information search using a Patricia tree, which is one type of a binary search tree.
[0002]
[Prior art]
The information retrieval system is a system for searching for a target information from a large amount of information accumulated in a predetermined format. One of the search methods used in the information search system is a so-called Patricia tree method. The Patricia (Patricia, "Practical Algorithm To Retrieve Information Code In Alphanumeric") tree is one of the well-known binary search trees. In a Patricia tree information retrieval system, an index of each information is created in advance by the Patricia tree. In addition, the corresponding information is extracted by searching this index. For example, in a Patricia tree-based full-text search system, an index is created by rearranging a semi-infinite partial character string starting from characters at all positions in each document in character code order, and the search key character string is The search is performed by determining whether the character string matches the infinite substring. At this time, in the actual search processing, the character string is treated as a bit string.
[0003]
An example of an information search method using the Patricia tree method will be described with reference to FIG. FIG. 7 is a diagram showing an example of the Patricia tree. In this case, the Patricia tree has a root N0, nodes N1 to N7, and 1s corresponding to the bit position values "0" and "1" to be compared at each node. The link (or edge) L1, L2, L3, L4,..., L16 is formed. In this case, 4-bit data “0000”, “0010”, “0100”,..., “0111” are registered as search keys in the nodes N1, N2, N3,. For example, when the data to be searched is “0010”, the node N1 connected by the link L1 corresponding to the leftmost bit value “0” of the data to be searched “0010” is selected as the next node in the root N0. You. At the node N1, a node N2 connected by a link L2 corresponding to the second bit value “0” from the left of the data “0010” is selected. At the node N2, the node N5 connected by the link L6 corresponding to the third bit value "1" from the left is selected. Then, at the node N5, the node N2 connected by the link L11 corresponding to the fourth bit value “0” from the left is selected again, and the value corresponding to the node N2 is extracted as a search result. As shown in FIG. 7, in the Patricia tree method, by placing a search key at each node, comparison of the entire search key during the search can be substantially reduced to one time.
[0004]
[Problems to be solved by the invention]
However, the above-described related art has the following problems. The first problem is that each node always has two link pointers to lower nodes. The reason is that it is necessary to link nodes corresponding to bit values “0” and “1” of a certain portion of the search key in order to form a binary tree. The second problem is that it is necessary to refer to information of a plurality of nodes at the same time to determine the end of the search. The reason is that in Patricia, the search is successful when the link from the node to the next node is upward, but the search position of the search key of the next node of the link destination is compared with the test position of the search key of the node. This is because it is necessary to save the information of the node. These problems have an effect of increasing the amount of memory used when constructing the Patricia tree and increasing the number of processing procedures for accessing information of a plurality of nodes.
[0005]
The present invention has been made in consideration of the above-described problems, and an information search method capable of reducing the number of processing steps and speeding up a node search and reducing the memory usage compared to the related art. And an apparatus.
[0006]
[Means for Solving the Problems]
In order to solve the above problem, the invention according to claim 1 is an information search method using a binary search tree, wherein a storage area for data corresponding to each node is replaced with a first storage area for storing data indicating a key. A second storage area for storing a link pointer to one other node; a third storage area for storing data indicating a link direction of the link pointer stored in the second storage area; And a fourth storage area for storing data indicating the position of the data to be inspected in the data stored in the storage area, and among the data corresponding to the respective nodes, a common node is defined as an upper node. A set of data corresponding to a pair of lower nodes is stored in a continuous storage area, and when a search process is performed for each node, the value stored in the third storage area is changed to a first predetermined value. If the second It is determined that the node indicated by the link pointer stored in the storage area is the node to be searched, and the value stored in the third storage area is a second predetermined value different from the first predetermined value , The next processing is performed based on the data at the position specified by the data in the fourth storage area of the data in the first storage area and the link pointer stored in the second storage area. A link pointer to a lower node to be performed is determined. According to a second aspect of the present invention, when a search process is performed for each node, the value stored in the third storage area is the first predetermined value. When the link pointer is not stored, it is determined that the search has failed.
[0007]
According to a third aspect of the present invention, when determining a link pointer to a lower node to be processed next, the position of the data specified by the data in the fourth storage area of the data in the first storage area is determined. When the data has a third predetermined value, the link pointer stored in the second storage area is used as a link pointer to a lower node, and the data in the first storage area is stored in the fourth storage area. When the data at the position specified by the data is a fourth predetermined value different from the third predetermined value, a predetermined fifth predetermined value is stored in the link pointer stored in the second storage area. A value obtained by adding the value is used as a link pointer to a lower node. According to a fourth aspect of the present invention, the data storage area corresponding to each of the nodes further has a fifth storage area for storing a pointer to each node unique information, and is stored in the third storage area. The stored value is the first predetermined value, and the pointer to the node unique information is stored in the fifth storage area corresponding to the node storing the data indicating the key in the first storage area. It is characterized by the following. According to a fifth aspect of the present invention, the value stored in the third storage area is the second predetermined value, and the value stored in the second storage area is stored in the first storage area. A pointer to the same node unique information as the link destination node is stored in the fifth storage area corresponding to the node storing the link pointer corresponding to the node storing the data indicating the key. It is characterized by.
[0008]
According to a sixth aspect of the present invention, in the information retrieval apparatus using a binary search tree, a first storage area for storing data indicating a key and a second storage for storing a link pointer to one other node. An area, a third storage area for storing data indicating the link direction of the link pointer stored in the second storage area, and a position of data to be inspected in the data stored in the first storage area. And a fourth storage area for storing data. The fourth storage area has a data storage area corresponding to each node, and among the data corresponding to each node, a common node is set as an upper node. A storage unit for storing a set of data corresponding to a pair of lower nodes in a continuous storage area, and a value stored in a third storage area when a search process is performed for each node. Is the value of Means for determining that the node indicated by the link pointer stored in the second storage area is a node to be searched, and that the value stored in the third storage area is a first predetermined value. If the second predetermined value is different from the data in the first storage area, the data at the position specified by the data in the fourth storage area and the link pointer stored in the second storage area Means for determining a link pointer to a lower node to be processed next based on
[0009]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is an explanatory diagram showing the structure of the nodes of the Patricia tree in the present embodiment. Referring to FIG. 1, in the present invention, a node 2a of the Patricia tree includes a search key 2a1, a link pointer 2a2, a link direction bit 2a3, a key check position 2a4, and a pointer 2a5 to node (entry) unique information. Similarly, the other nodes 2b1 and 2b2 also store the search keys 2b11 and 2b21, the link pointers 2b12 and 2b22, the link direction bits 2b13 and 2b23, the key inspection positions 2b14 and 2b24, and the pointers 2b15 and 2b25 to the node-specific information. Include each. The Patricia tree also holds the node length 29 as a constant in a predetermined storage area.
[0010]
The search keys 2a1, 2b11, and 2b21 are used as search keys constituting a Patricia tree, respectively. The link pointers 2a2, 2b12, and 2b22 store pointers to upper nodes or lower nodes, respectively. The link direction bits 2a3, 2b13, 2b23 define the properties of the pointers stored in the link pointers 2a2, 2b12, 2b22, respectively. When the link direction bits 2a3, 2b13, 2b23 are "0", the link pointers 2a2, 2b12, 2b22 Stores NULL or the head pointer of the upper node, and when the link direction bits 2a3, 2b13, 2b23 are "1", the link pointers 2a2, 2b12, 2b22 store the head pointer of the lower left node. In the example shown in FIG. 1, the node 2a holds a search key constituting a Patricia tree as the search key 2a1, and stores a pointer to the lower left node 2b1 as the link pointer 2a2. In this case, "1" is stored in the link direction bit 2a3.
[0011]
The key inspection positions 2a4, 2b14, and 2b24 store inspection positions (bit positions) starting from the left side in the search target 28 in each node of the Patricia tree. The pointers 2a5, 2b1, and 2b2 to the node-specific information respectively store pointers to management information used in processing after the search is completed successfully. The pointers 2a5, 2b1, and 2b2 to the node unique information are not referred to during the search processing. In the present embodiment, each node except for a root (root) node is arranged such that two nodes always occupy a continuous area in the storage area like the lower left node 2b1 and the lower right node 2b2 in FIG. . Therefore, by adding the node length 29 to the link pointer 2a2 storing the pointer to the lower left node 2b1, the value of the pointer of the lower right node 2b2 can be obtained. The search target 28 stores a value to be searched with the same size as the search keys 2a1, 2b11, and 2b21. Here, each data is treated as a bit string. The node length 29 stores the length (data length) of the nodes 2a, 2b1, and 2b2. However, the method of arranging the two nodes is not limited to the above. For example, the positions of the lower right node and the lower left node are interchanged, and the value of the link pointer corresponds to the lower right node. May be obtained to obtain a value corresponding to the lower left node.
[0012]
Next, a search operation related to the node 2a shown in FIG. 2 will be described with reference to a flowchart shown in FIG. The search processing according to the present embodiment is executed by a CPU (central processing unit) having a predetermined storage device. The data of the search target, each node, and the node length are stored in the storage device during the search processing. Further, the program executed by the CPU can be distributed via a computer-readable recording medium or a communication line. In the configuration of FIG. 2, the search operation for the search target 28 and the node 2a starts by first examining the link direction bit 2a3 of the node 2a (step S1 in FIG. 4). If the link direction bit 2a3 is "0", the link pointer 2a2 is checked next (step S6). If the link direction bit 2a3 is "0" and the link pointer 2a2 is NULL, the corresponding node does not exist, and the search fails and the search operation ends. If the link direction bit 2a3 is "0" and the link pointer 2a2 is other than NULL, the node pointed to by the pointer is a node having a search key that matches the search target 28, and therefore the node pointed to by the link pointer 2a2 (in this case, shown in FIG. The contents of the upper-level node that has not been read are read (step S7), and node-specific information pointed to by the pointer to the node-specific information is obtained (step S8).
[0013]
On the other hand, in FIG. 4, if the link direction bit 2a3 is "1" in step S1, the search is continued. The value of the position indicated by the key inspection position 2a4 starting from the left side of the search target 28 is checked (steps S2 and S3). If the value of the position indicated by the key inspection position 2a4 in the inspection target 28 is "1", it means that the right lower node of the Patricia tree is to be traced. Therefore, a value obtained by adding the node length 29 to the link pointer 2a2 is used as the pointer. Then, the content pointed to by the pointer is newly read as the content of the lower right node (step S4). If the value of the position indicated by the key inspection position 2a4 of the search target 28 is "0", it means that the left lower node of the Patricia tree is to be traced, so that the content pointed to by the link pointer 2a2 is read as the content of the lower left node (step S5). ). The search operation from step S1 to step S5 is repeated until the link direction bits 2a3, 2b13, 2b23,... Become "0".
[0014]
Next, referring to the Patricia tree representation shown in FIGS. 2 and 3 and the flowchart of FIG. 4, the operation of the present embodiment will be described in detail with a specific example. In this example, it is assumed that three lower nodes in the Patricia tree are configured as shown in FIGS. FIG. 2 is a diagram showing a value of each node and a mutual positional relationship, and FIG. 3 is a Patricia tree representation thereof. The key of the inspection target 30 corresponding to the search target 28 in FIG. 1 is set to “00110”, and the node length 31 corresponding to the node length 29 in FIG. 1 is set to the node length of each node. Nodes 3a1 and 3a2 shown in FIG. 2 are lower left and lower right nodes linked from an upper node (not shown). However, the illustration of the node 3a2 is omitted in FIG.
[0015]
2, in the node 3a1, the search key 3a11 contains data "00100", the link pointer 3a12 contains the pointer to the node 3b1 (link L1 in FIGS. 2 and 3), and the link direction bit 3a13 contains "1". “3” is stored in the search position 3a14, and a pointer to the node unique information 4a is stored in the pointer 3a15 to the node unique information. In the node 3b1, NULL is stored in the link pointer 3b12, and "0" is stored in the link direction bit 3b13. In the node 3b2, the data “00110” is stored in the search key 3b21, the pointer (link L2) to the node 3c1 is stored in the link pointer 3b22, “1” is stored in the link direction bit 3b23, “4” is stored in the key search position 3b24, and , A pointer to the node unique information 4a is stored in the pointer 3b25 to the node unique information.
[0016]
In the node 3c1, a pointer (link L3) to the node 3a1 is stored in the link pointer 3c12, and “0” is stored in the link direction bit 3c13. In the node 3c2, the data “00111” is stored in the search key 3b21, the pointer (link L4) to the node 3d1 is stored in the link pointer 3c22, “1” is stored in the link direction bit 3c23, “5” is stored in the key search position 3c24, and , The pointer to the node unique information 4c is stored in the pointer 3c25 to the node unique information. In the node 3d1, a pointer (link L6) to the node 3b2 is stored in the link pointer 3d12, and “0” is stored in the link direction bit 3d13. In the node 3d2, a pointer (link L5) to the node 3c2 is stored in the link pointer 3d22, and “0” is stored in the link direction bit 3d23.
[0017]
Next, a search operation regarding the nodes shown in FIGS. 2 and 3 will be described with reference to a flowchart shown in FIG. Now, it is assumed that the given search target 30 “00110” is compared with the node 3a1. In this case, first, the link direction bit 3a13 is checked (step S1). Since this value is "1", the search is continued. When the key search position 3a14 is examined next to follow the lower node, the value is "3", so the third value from the left of the search target 30 is examined (steps S2 and S3). Then, since the value is "1", in order to follow the lower right node 3b2, the content is read as the pointer to the next node with the value obtained by adding the value of the node length 31 to the link pointer 3a12, and the node 3b2 is obtained as a new node ( Step S5).
[0018]
Next, the link direction bit 3b23 is checked (step S1). Since the value is "1", the search is continued. Since the value of the key search position 3b24 is "4", the fourth value from the left of the search target 30 is checked (steps S2 and S3). Then, since the value is "1", the content is read as a pointer to the next node by adding the value of the node length 31 to the link pointer 3b22 in order to follow the lower right node 3c2, and the node 3c2 is obtained as a new node (step S5).
[0019]
Similarly, the lower left node 3d1 is obtained from the search target 30 and the key inspection position 3c24. When the link direction bit 3d13 of this node is examined (step S1), the value is "0", and the link pointer 3d12 is examined next (step S6). ). Then, since the value is not NULL, the node 3b2 indicated by the link pointer 3d12 becomes the search target node, and the contents of the node 3b2 are read (step S7). Finally, the node specific information pointed to by the pointer 3b25 to the node specific information is obtained (step S8), and the search ends.
[0020]
Next, another embodiment of the present invention will be described in detail with reference to FIGS. Referring to FIG. 5, the present embodiment is different from the above embodiment in that the nodes 3a1, 3b2, and 3c2 whose link direction bit is “1” and that has a search key are respectively node unique information 4a. , 4b, 4c, and the link pointers 3a12, 3b22, 3c22 to other nodes, but the link direction bit is "0", and Nodes 3c1, 3d1, and 3d2 that have links to nodes 3a1, 3b2, and 3c2 that have keys are also pointers 3c15, 3d15 that point to the same node-specific information 4a, 4b, and 4c as nodes 3a1, 3b2, and 3c2 that are links. It differs in having 3d25.
[0021]
The overall operation of the present embodiment will be described in detail with reference to the flowcharts of FIGS. The operation in this embodiment shown in steps S1 to S5 in FIG. 6 is the same as the operation in steps S1 to S5 in the above embodiment shown in FIGS. The flowchart shown in FIG. 6 is obtained by omitting the processing in step S7 of the flowchart shown in FIG. In the embodiment shown in FIG. 2, when the link direction bit is “0” and the link pointer is not NULL, the node specific information is obtained after further reading the search target node indicated by the link pointer. In the present embodiment, a pointer to node-specific information is set for a node whose link direction bit is “0” and whose link pointer is not NULL.
[0022]
Next, a description will be given using a specific example. In the flow shown in FIG. 5, when the search process is performed for the key “00110” of the search target 30 in the same manner as in FIG. 2, when the node 3d1 is obtained, the link direction bit 3d13 becomes “0”. Check (steps S1 and S6 in FIG. 6). Then, since the value of the link pointer 3d12 is not NULL, the node 3d1 has a link pointer pointing to the search target node. Then, the node unique information 4b pointed to by the pointer 3d15 to the node unique information having the same value as the search target node is read (step S7), and the search is successful.
[0023]
In the present embodiment, it is necessary to configure a node in which the link direction bit is “0” and the link pointer is not NULL so that the node has the same pointer to the node specific information as the node indicated by the link pointer. Since the node reading process can be reduced by one step, there is a new effect that the search process can be performed at higher speed.
[0024]
As described above, according to the present invention, it is possible to provide a configuration in which a node search can be performed at higher speed in a Patricia tree, which is one type of a binary search tree, as compared with the related art. The features of the present invention are summarized as follows. In FIG. 1, in the present invention, for a node 2a constituting a Patricia tree, only one link pointer to a lower node required in a normal binary tree is provided as a link pointer 2a2. The link pointer 2a2 is a pointer of the lower node in the left direction, and is also interpreted as a pointer of the lower node in the right direction by adding the node length 28. The selection of the link destination is distinguished by the value indicated by the key inspection position 2a4 starting from the left in the search key 2a1.
[0025]
In the search processing, the link pointer 2a2 is checked first, and if NULL, the search fails and the processing ends. If it is other than NULL, the link direction bit 2a3 is checked next. If "0", the node indicated by the pointer is the node to be searched, and the search is successful. If "1", the search is continued, and a pointer to the next lower node is determined by a combination of the value of the position indicated by the key check position 2a4 in the search target 28 and the link pointer 2a3. As described above, the continuation / success / failure of the Patricia tree search can be determined only by the information on the node without referring to the storage area other than the node and saving the contents of the node. The node search can be performed at high speed by reducing the time and the number of processing procedures associated with the use of a plurality of storage areas.
[0026]
【The invention's effect】
A first effect of the present invention is that a node search can be performed at high speed in a Patricia tree. The reason is that each node has a link direction bit so that search continuation / success / failure can be determined only by information on the node. A second effect is that the amount of memory used when configuring a Patricia tree can be reduced. The reason is that the left and right lower nodes are always configured to occupy a continuous storage area, so that each node only needs to have one pointer to the left and right lower nodes by holding the node length information independently. That's why.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram showing an example of the structure of a node of a Patricia tree in the information search method of the present invention.
FIG. 2 is an explanatory diagram showing values of each node and a mutual positional relationship according to the embodiment of the present invention;
FIG. 3 is an explanatory diagram showing each node shown in FIG. 2 in a Patricia tree expression.
FIG. 4 is a flowchart showing an information search operation according to an embodiment of the present invention.
FIG. 5 is an explanatory diagram showing a modification of the configuration of each node shown in FIG. 2;
FIG. 6 is a flowchart showing an information retrieval operation using the node configuration shown in FIG. 6;
FIG. 7 is an explanatory diagram showing an example of the structure of a node of a Patricia tree in a conventional information search method.
[Explanation of symbols]
2a, 2b1, 2b2, 3a1, 3a2, 3b1, 3b2, 3c1, 3c2, 3d1, 3d2... Nodes 2a1, 2b11, 2b21, 3a11, 3b21, 3c21. , 3d12, 3d22... Link pointers 2a3, 2b13, 2b23, 3a13, 3b13, 3b23, 3c13, 3c23, 3d13, 3d23... Link direction bits 2a4, 2b14, 2b24, 3a14, 3b24, 3c24. , 3a15, 3b25, 3c25... Pointers 28, 30... To be searched 29, 31... Node length

Claims (6)

In an information search method using a binary search tree,
A storage area for data corresponding to each node is stored in a first storage area for storing data indicating a key, a second storage area for storing a link pointer to one other node, and a second storage area. A third storage area for storing data indicating the link direction of the stored link pointer, and a fourth storage area for storing data indicating the position of data to be inspected in the data stored in the first storage area Consisting of
A set of data corresponding to a pair of lower nodes having a common node as an upper node among data corresponding to the respective nodes is stored in a continuous storage area,
When performing search processing for each node,
When the value stored in the third storage area is the first predetermined value, it is determined that the node indicated by the link pointer stored in the second storage area is a node to be searched,
When the value stored in the third storage area is a second predetermined value different from the first predetermined value, the data in the first storage area is designated by the data in the fourth storage area. An information retrieval method which determines a link pointer to a lower node to be processed next, based on data at a position to be processed and a link pointer stored in a second storage area. When the search processing is performed for each node, the value stored in the third storage area is the first predetermined value, and the link pointer is not stored in the second storage area 2. The information search method according to claim 1, wherein it is determined that the search has failed. When determining the link pointer to the lower node to be processed next, the data at the position specified by the data in the fourth storage area of the data in the first storage area is a third predetermined value. In this case, the link pointer stored in the second storage area is used as the link pointer to the lower node, and the data in the first storage area is located at the position specified by the data in the fourth storage area. When the data is a fourth predetermined value different from the third predetermined value, a value obtained by adding a predetermined fifth predetermined value to the link pointer stored in the second storage area is set to the lower node. 3. The information retrieval method according to claim 1, wherein a link pointer to the information is used. The data storage area corresponding to each of the nodes further has a fifth storage area for storing a pointer to each node-specific information,
A value stored in the third storage area is the first predetermined value, and a node is stored in a fifth storage area corresponding to a node storing data indicating a key in the first storage area. 4. The information search method according to claim 1, wherein a pointer to unique information is stored. Further, the value stored in the third storage area is the second predetermined value, and data indicating a key is stored in the first storage area in the second storage area. 5. The pointer to the same node unique information as the link destination node is stored in the fifth storage area corresponding to the node storing the link pointer corresponding to the current node. Information retrieval method. In an information search device using a binary search tree,
A first storage area for storing data indicating a key, a second storage area for storing a link pointer to one other node, and data indicating a link direction of the link pointer stored in the second storage area. Data corresponding to each node composed of a third storage area for storing and a fourth storage area for storing data indicating the position of the data to be inspected in the data stored in the first storage area And a set of data corresponding to a pair of lower nodes having a common node as an upper node among data corresponding to the respective nodes is stored in a continuous storage area. Storage means;
When performing search processing for each node,
Means for determining , when the value stored in the third storage area is a first predetermined value, a node indicated by the link pointer stored in the second storage area to be a node to be searched; ,
When the value stored in the third storage area is a second predetermined value different from the first predetermined value, the data in the first storage area is designated by the data in the fourth storage area. An information retrieving apparatus comprising: means for determining a link pointer to a lower node to be processed next, based on data at a position to be processed and a link pointer stored in a second storage area.

Images