CN101853310A - Method for producing preorder and postorder code of single traversing tree - Google Patents

Abstract

The invention discloses a method for simultaneously constructing a preorder code and a postorder code of an XML (Extensive Makeup Language) document through single traversing, belonging to the field of data structures and algorithms. The invention combines same traversing orders in the preorder code and the postorder code by separating the traversing order and the coding order of an XML node, has the key technical point of correctly locating the opportunity of going in and out the node, and simultaneously maintains two independently increasing preorder coding order and postorder coding order. When single scan to an XML tree is finished, each node can obtain a unique preorder code and a unique postorder code per se. In the invention, the consumption of two-time scan is lowered to single scan, the time of the method for producing the preorder code and the postorder code by single scan is halved when the data quantity is large, and the process of the XML document constructing an index is greatly accelerated.

Description

The method of producing preorder and postorder code of single traversing tree

Technical field

The invention provides a kind of method of the XML of foundation index, be specifically related to a kind of single ergodic XML document and generate front and back preface Methods for Coding, belong to data structure and algorithm field.

Background technology

Existing XML index technology with the XML data cell as recorded and stored, preserve the positional information that helps determine structural relation between node simultaneously, positional information is divided into two classes usually, one class is the sequence number of node in certain traversal method gained character string, and another kind of is the routing information of node in XML document.Index coded system based on the front and back preface can intactly reflect the internodal structural relation of XML, and then XML document is expressed as a sequence of being made up of node.

Front and back preface coding is a kind of interval coded system, its basic thought is with the interval (pre of the sequence in formerly preface ergodic sequence and the postorder traversal sequence to forming, post) as the positional information of node, its base index record form is (s, pre, post), wherein s is the tag attributes of node in the XML tree.The mode of front and back preface coding often is applied to make up the index of XML document.

Usually the front and back preface coding that obtains XML all needs to carry out preorder traversal and twice scanning of postorder traversal, and the time cost that twice scanning is consumed when XML document is very big is huge.

Summary of the invention

The object of the present invention is to provide a kind of method, realize preorder and postorder coding simultaneously by single sweep operation XML tree, so as to solving the time loss problem that twice common scanning brings.

Principle of the present invention is that the traversal preface of XML node and code sequence are separated, and merges identical traversal preface in preamble and the postorder coding then, and then realizes the scheme of single sweep operation.The XML sequence node shape that obtains in the preface in traversal is as " go into A, go into B, go into C, go out C; go into D, go out D, go out B, go into E; go out E, go out A ", and preamble is the opportunity of triggering coding, i.e. A with the ingress, B, C, D, E, and postorder coding is the opportunity of triggering coding with the egress, i.e. C, D, B, E, A specifically sees Fig. 2.Can travel through (or postorder coding traversal) scheme with reference to preamble to XML traversal of tree process, crucial technology point for correctly locate, opportunity of egress, and safeguard two independent preamble preface and postorder code sequences that increase simultaneously, each node all will obtain unique preamble and the postorder coding of oneself when finishing the single pass that XML is set.In program code, set up enter recursive function forward and backward to be respectively opportunity, and state that two global variables are used for preserving the preamble preface and the postorder code sequence of current growth into, egress.

Technical scheme of the present invention is as follows:

Defined function V, its parameter for the tree node n, the execution flow process of this function as shown in Figure 1, its implementation is as follows:

1) if. parameter n is null, then withdraws from this function; Otherwise carry out 2);

2). make up preamble;

3). parameter n is defined as its left child node, recursive call function V;

4). make up the postorder coding;

5). make up preamble;

6). parameter n is defined as its right child node, recursive call function V;

7). make up the postorder coding;

8). function finishes.

The present invention realizes preorder and postorder Methods for Coding simultaneously by the single sweep operation XML document, the consumption of twice scanning is reduced to once, when data volume was very big, the preface Methods for Coding had reduced the time overhead of half before and after single sweep operation generated, and had quickened the process of XML document index building greatly.

Description of drawings

Fig. 1 is for carrying out the process flow diagram that the single traverse tree generates front and back preface coding;

The example of Fig. 2 for a tree is traveled through.

Embodiment

The present invention is further elaborated with a specific embodiment below.

Fig. 2 is the example of preface coding before and after a single sweep operation generates, and this tree has 5 nodes, and wherein A is a root node.Carry out ergodic process through method provided by the invention, can draw following result:

This traversal of tree sequence is: go into A, go into B, go into C, go out C, go into D, go out D, go out B, go into E, go out E, go out A; The sequence of preamble is: A, B, C, D, E; The sequence of postorder coding is: C, D, B, E, A.Therefore realized the single ergodic tree function of coding front and back preface simultaneously.

It should be noted that at last the purpose of publicizing and implementing example is to help further to understand the present invention, but it will be appreciated by those skilled in the art that: without departing from the spirit and scope of the invention and the appended claims, various substitutions and modifications all are possible.Therefore, the present invention should not be limited to the disclosed content of embodiment, and the scope of protection of present invention is as the criterion with the scope that claims define.

Claims (2)

1. one kind makes up XML preorder and postorder Methods for Coding, it is characterized in that, described method to the traversal number of times of XML document for once; Its implementation is: defined function V, and its parameter is the node n of tree, the implementation method of this function is as follows:

1) if. parameter n is null, then withdraws from this function; Otherwise carry out 2);

2). make up preamble;

3). parameter n is defined as its left child node, recursive call function V;

4). make up the postorder coding;

5). make up preamble;

6). parameter n is defined as its right child node, recursive call function V;

7). make up the postorder coding;

8). function finishes.

2. the method for claim 1 is characterized in that, described preamble and postorder coding respectively are kept in the global variable; Described structure preamble and structure postorder coding are meant the maintenance to this global variable.