1. (b) Tree representation
Early Profile Pruning on XML-aware Publish-Subscribe Systems
Mirella M. Moro, Petko Bakalov, Vassilis J. UCR
Full version appears in the Proceedings of the 33rd International Conference on Very Large Data Bases (VLDB 2007)
1 Motivation
3 FSM based bottom up approach for XML filtering (BUFF)
Theorem: If a query tree Q is a subgraph of a document tree D then the Prüfer sequence Q is a subsequence of the Prüfer sequence of D
Increased popularity of Publish-subscribe systems – an important class of content-based dissemination systems where the message transmission is defined by the message content, rather than its destination IP address.
2.1 Bottom-up vs. Top-down filtering
We can derive two new sequences
Upper bound U: for each position take largest element
Lower bound L: for each position take smallest element
L and U form a Sequence Envelope.
Top-down approach: (i.e. in-order traversal or depth first order): advancing the state machine for each XML element (or attribute) read.
Bottom-up approach: This approach takes into consideration the fact that an XML document has its more selective elements in the leaves Q1 a b c d Q2 Q4 e f h Q5 Q6 g
(b) Queries
(d) BUFF
(c) NFA 1 2 5 7 10 3 4 6 8 9 11 13 12 14 Q3
(a) Document
root
Sequence envelopes can be nested forming BoXFilter tree
2.2 BUFF algorithm
The document is parsed through a SAX parser, which triggers events for specific marks (tags) in the XML document
The machine keeps a runtime stack that stores the current document path being processed.
For each opening tag, the respective element is pushed to the stack
For each closing tag, an element is popped from and is employed to trigger a set of transitions within the NFA.
2 System Description
Participants in the system:
Publisher: generates messages outside of the system
Subscribers: announce their interest by submitting profiles
Matching process: in charge of finding which messages satisfy which profile
Profile Index
Profiles P1 P2 P3
Prüfer
Sequence
Profile
Manager
Matching
Algorithm
Input
Documents
(queries)‏
Matched
Module
(a) Document and BUFF a
<a> b
<b> c
<c> d
<d>
</e> 1 d4 a1 b2 c3 d7 b5 c6 e8
f10 e9 2 e 3 4 Q1 5 6 f 7 8 Q2
(b)‏
</d>
(c)‏
(d)‏
(e)‏
1,2
</f>
(f)‏
(g)‏
</c>
3,6
1,2,5
(h)‏
The profiles in the system are organized in BoXFilter tree. Documents are traversed thought the tree
Publisher
Matching algorithm
Documents
Profile
Submit,
Modify
Result
Documents
There are two variations of the filtering algorithm
Sequential – documents are processed one by one
Batch processing – documents are organized in a tree like the queries and both trees are joined.
After the traversal, there is a verification step
4 Bounding-based XML Filtering (BoxFilter)
The data is exchanged in XML format.
Nodes - correspond to elements, attributes or text values
Edges - represent immediate element-sub element or element-value relationships
5 Results
Prüfer Sequence: A unique sequential encoding of a enumerated and labeled tree
Algorithm:
Iteratively removes nodes from the tree.
At each iteration, the algorithm finds and removes the leaf with the smallest number and adds to the Prüfer sequence the number of that leaf's parent. A 1 B 2 D 5 C 3 E 6 F 8 4 7 9
Prüfer Sequence
<Bib>
<article vol=“7” no=“11”>
<title>t1</title>
<author>
<last>DeWitt</last>
<mi>J</mi>
<first>David</first>
</author>
<journal>TPDS</journal>
<year>1996</year>
</article>
<article>
<title>t2</title>
<last>Florescu</last>
<first>Daniela</first>
<proceedings>SIGMOD
</proceedings>
<year>2006</year>
</Bib>
Bib
article
title
journal
author
last
first
David
DeWitt
TPDS t1
proceedings
Daniela
Florescu
SIGMOD t2 mi J
year
1996
2006 no 11
vol 7
(a)‏
(b)‏
(c)‏
(b) Tree representation
The user profiles are expressed in XML query language (XPath, XQuery)
XML query contains
structural constraints
value-based constraints
(a) Document
1.03
0.95
0.35
article
proceedings
conf
author
last
Structural constraints:
Tree pattern: