Requests to Tsong-Li

1
Requests to Tsong-Li

• 1. Related work at end of each section
• 2. Screen dumps of treebase at end of treesearch
  section (youll see where)
• 3. Web addresses at the very end.

2
Searching for and ComparingTrees and Graphs

• Dennis Shasha, shasha_at_cs.nyu.edu
• Courant Institute, NYU
• Joint work with
• Kaizhong Zhang and Jason Wang

3
Philosophy

• Trees and graphs represent data in many domains
  in linguistics, chemistry, and even maybe the
  web.
• Question why cant I search for trees or graphs
  at the speed of keyword searches?
• Why cant I compare trees (or graphs) as easily
  as I can compare strings?

4
Tree Searching

• Given a small tree t is it present in a bigger
  tree T?

5
What does present mean?

• Preserving sibling order or not
• Preserving ancestor order
• Preserving distance
• Mismatches

6
Sibling Order

• Order of children of a node

A
A
?
B
B
C
C
7
Ancestor Order

• Order between children and parent.

C
A
?
A
B
C
B
8
Ancestor Distance

• Can children become grandchildren

A
A
?
X
B
B
C
C
9
Mismatches

• Can there be relabellings, inserts, and deletes
  (Tolstoy problem)

A
A
how far?
C
B
X
C
10
Bottom Line

• There is no one definition of mismatch or subtree
  (Tolstoy problem). You must choose the package
  that suits you.
• I will tell you about three.

11
TreeSearch Query Language

• Query language is simply a tree decorated with
  single length dont cares (?) and variable length
  dont cares ().

A
gt 0, on each side
?
1

C
D
B
12
Exact Match

• Query matches exactly if contained regardless of
  sibling order or other nodes

X
A
A
Y
Q
X
?

W
B

Z
D
C
D
U
B
C
13
Inexact Match

• Inexact match if missing or differing node
  labels. Higher differences cost more.

X
A
A
Y
Q
X
?
Differ by 1
W

B
Z
E
C
D
U
B
C
14
Treesearch Conceptual Algorithm

• Take all paths in query tree.
• Find out where each path is in the data tree.
• So notion of distance is number of paths that
  differ. Higher nodes are more important.
• Implementation suffix array. A few seconds on
  several thousand trees.

15
Treesearch Review

• Ancestor order matters.
• Sibling order doesnt.
• Dont cares and ?
• Distance metric is based on numbers of path
  differences.
• Sister system built by Divesh and Sihem at Bell
  Labs that allows terms to be generalized

16
Tsong-Li screen dumps of treebase then related
work
17
Tree Edit

• Order of children matters

A
A
A-gtA del(B) ins(B)
B
B
C
C
18
Tree Edit in General

• Operations are relabel A-gtA, delete (X), insert
  (B).

A
A
A-gtA del(B) ins(B)
B
X
C
C
C
C
19
Review of Tree Edit

• Generalizes string editing distance for trees, a
  dynamic programming algorithm.
• O(T1 T2 depth(T1) depth(T2))
• The basis for XMLdiff.
• Also has and best removal of subtrees.

20
Tsong-Li related work here
21
Graph Edit

• Thesis work of Rosalba Giugno.
• Find a small graph (with and ?) in a big graph.
• Doesnt work fast if query graph is big because
  graph subisomorphism is exponential.

22
Example of GraphGrep

• Query graph has nodes and dont cares

A
C
D

B
23
Summary of Tools

• Why cant tree and graph search be like keyword
  search?
• We are getting there and will provide software if
  you are interested.
• Current downloads of about 50.