Indexing XML Data in RDBMS using ORDPATH

Transcription

1 Indexing XML Data in RDBMS using ORDPATH Microsoft SQL Server 2005 Concepts developed by: Patrick O Neil,, Elizabeth O Neil, (University of Massachusetts Boston) Shankar Pal,, Istvan Cseri,, Oliver Seeliger,, Gideon Schaller, Leo Giakoumakis,, Vasili Zolotov,, Nigel Westbury (Microsoft Corporation)

2 XML Data Model Sample XML Data (serialized form): <BOOK ISBN= > <SECTION> <TITLE> Bad Bugs</TITLE> Nobody loves bad bugs. <FIGURE CAPTION= Sample bug /> </SECTION> <SECTION> <TITLE> Tree Frogs </TITLE> All right-thinking people <BOLD> love </BOLD> tree frogs. </SECTION> </BOOK> 5. Juli 2006 Stephan Müller 2

3 XML Data Model XML Document / Fragment - Properties: 1 Book 2 ISBN 3 Section 8 Section Hierarchy 4 Title 5 Nobody 6Figure Caption 7 Title All right Bold Frogs Document Order: 1 < 2 < 3 < 4 < 5 <.. < 11 < Juli 2006 Stephan Müller 3

4 XML Data Stored in a Relational Database SQL Command: CREATE TABLE docs ( id INT PRIMARY KEY, xdoc XML ); Created docs Table: ID XDOC 1 2 XML Fragment as BLOB XML Document as BLOB SQL with embedded XQuery and XPath: XML Fragment as BLOB SELECT id, xdoc.query( for $s in /BOOK[@ISBN= ]//SECTION return <topic> { data($s/title) } </topic> ) FROM docs; 5. Juli 2006 Stephan Müller 4 7

5 ORDPATH

6 What we expect from a labeling scheme: Introduction Support for structural fidelity (Hierarchy + Document Order) Support for efficient structural modifications to the XML tree - insert sub-tree - delete sub-tree without relabeling!!! - move sub-tree Support for high-performance query plans for native XML queries using relational primitives Independence of XML schemas typing XML instances 5. Juli 2006 Stephan Müller 6

7 1 Book Example of an Initial Load 1.1 ISBN Section 1.3 Section Hierarchy Title Nobody Figure Title All right Bold Frogs Caption Primary Index: infoset ORDPATH 1 TAG 1 (BOOK) NODE_TYPE VALUE Null (ISBN ) 2 (Attribute) ' ' 3' (SECTION) Null (TITLE) 'Bad Bugs' (Value( Value) 'Nobody loves bad bugs' (FIGURE) Null Document Order: (CAPTION) 3 (SECTION) 2 (Attribute) 'Sample bug' Null 1 < 1.1 < 1.3 < < < (TITLE) -- 4 (Value( Value) 'Tree frogs' 'All right-thinking thinking people' 5. Juli (BOLD) 'love' (Value( Value) 'tree frogs'

8 L i /O i Pair Design

9 L i /O i Pair Design ORDPATH Example Value: Li /Oi Pair Desgin: L 0 O 0 L 1 O 1 L K O K ORDPATH bit pattern: We need a prefix-free L i encoding 5. Juli 2006 Stephan Müller 9

10 Prefix Free Encoding of the L i Bitstrings (using the Fano Condition) 5. Juli 2006 Stephan Müller 10

11 Li /Oi Pair Design ORDPATH Example Value: Using Li values from Figure 3.2a L 0 = 3 O 0 = 1 L 1 = 3 O 1 = 5 L 2 = 3 O 2 = 3 L 3 = 4 O 3 = -9 L 4 = 4 O 4 = ORDPATH bit pattern (Figure 3.2a) 5. Juli 2006 Stephan Müller 11

12 Li /Oi Pair Design Advantages of comparing ORDPATH Values: Determination of ancestor descendent relationships for any two ORDPATHs is very easy. Easy determination of the distance between two ORDPATHs. Simple bitstring (or byte-by by-byte) comparison yields document order. 5. Juli 2006 Stephan Müller 12

13 Descendants of a given Context Node Context Node ( cn = 1.3 ) 1 Book 1.1 ISBN Section 1.3 Section Title Nobody Figure Title All right Bold Frogs Caption Juli 2006 Stephan Müller 13

14 Descendants of a given Context Node SQL Query: Infoset Table: SELECT Ordpath FROM infoset WHERE 1.3 < Ordpath (cn) AND 1.4 > Ordpath (cn+1) ORDPATH TAG NODE_TYPE VALUE 1 1 (BOOK) Null (ISBN ) 2 (Attribute) ' ' 3' (SECTION) Null (TITLE) 'Bad Bugs' (Value( Value) 'Nobody loves bad bugs' (FIGURE) Null (CAPTION) 2 (Attribute) 'Sample bug' (SECTION) Null (TITLE) Tree frogs' (Value( Value) All right-thinking thinking people' (BOLD) love' (Value( Value) tree frogs' 14

15 Arbitrary Inserts

16 Arbitrary Insertions Rightmost / Leftmost Insertion: 3.5 Parent Child Child1 Child Child Juli 2006 Stephan Müller 16

17 Arbitrary Insertions Careting in nodes between two existing nodes Juli 2006 Stephan Müller 17

18 Arbitrary Insertions Careting in nodes between two existing nodes 3.5 Parent Child1 Child3 Child6 Child5 Child4 Child Juli 2006 Stephan Müller 18

19 Note: Multiple levels of carets are extremely rare in practice. Comment Advantage: Insertions require no relabelings of old nodes We avoid updates to primary key values which would involve the primary index and all secondary indexes. 5. Juli 2006 Stephan Müller 19

20 Conclusion ORDPATH is a hierarchical prefix-based labeling scheme. provides efficient access to subtrees. provides all kinds of modifications. 5. Juli 2006 Stephan Müller 20