Web Data

1
Web Data

• Semistructured data
• XML data

2
Classes of XML Documents

• Structured
• Un-normalized relational data
• Ex product catalogs, inventory data, medical
  records, network messages, logs, stock quotes
• Mixed
• Structured data embedded in large text fragments
• Ex On-line manuals, transcripts, tax forms
• Application may process XML in both classes
• Ex SOAP messages
• Header is structured payload is mixed

3
Structured Data HL7 Lab Report

• Health-care industry data-exchange format
• ltHL7gt
• ltPATIENTgt
• ltPID IDNum"PATID1234"gt
• ltPaNagtltFaNagtJoneslt/FaNagtltGiNagtWilliamlt/GiNagt
  lt/PaNagt
• ltDTofBigtltdategt1961-06-13lt/dategtlt/DTofBigt
• ltSexgtMlt/Sexgt
• lt/PIDgt
• ltOBX SetID"1"gt
• ltObsVagt150lt/ObsVagt
• ltObsIdgtNalt/ObsIdgt
• ltAbnFlgtAbove highlt/AbnFlgt
• lt/OBXgt
• ...

4
Mixed Data Library of Congress

• Documents of U.S. Legislation
• ltbill bill-stage"Introduction""gt
• ltcongressgt110th CONGRESSlt/congressgt
• ltsessiongt1st Sessionlt/sessiongt
• ltlegis-numgtH.R. 133lt/legis-numgt
• ltcurrent-chambergtIN THE HOUSE OF
  REPRESENTATIVESlt/current-chambergt
• ltaction date"June 5, 2008"gt
• ltaction-descgt
• ltsponsorgtMr. Englishlt/sponsorgt (for himself
  and ltcosponsorgtMr.Coynelt/cosponsorgt)
  introduced the following
• bill which was referred to the
  ltcommittee-namegtCommittee on Financial
  Serviceslt/committee-namegt ...
• lt/action-descgt

5
Wheres the XML Data?
6
Schemas
here lies our interest

• why ?
• XML to describe semantics
• semistructured data to improve processing
• what ?
• semistructured data foundational
• XML several concrete proposals

7
Schemas

• when ?
• semistructured data, XML a posteriori
• RDBMS a priori, to interpret binary data
• how ?
• semistructured data schema is independent
• XML schema is hardwired with the data

8
Outline

• schemas for semistructured data
• foundations
• schema extraction
• schemas for XML
• DTD
• XML-Schema
• RDF-Schema

9
Schemas An Example
Some database
10
Lower-Bound Schemas
Root
person
company
works-for
managed-by
Employee
Company
c.e.o.
name
address
name
string
11
Upper Bound Schemas
Root
person
company
works-for
managed-by
Employee
Company
c.e.o. employee
name address url
name phone position
description
string
Any
-
12
The Two Questions to Ask

• Conformance does that data conform to this
  schema ?
• Classification if so, then which objects belong
  to what classes ?

13
Schemas for Semistructured XML Data

• Motivations for considering schema
• Optimize query evaluation
• Improve storage efficiency
• Support index construction
• Facilitate the description of database content
• Facilitate query formulation
• Facilitate data integration.

14
Application 1 Improve Secondary Storage
Lower-bound schema
Store rest in overflow graph
15
Application 2 Query Optimization
select X.title from Bib._ X where X..zip
12345
select X.title from Bib.book X where
X.address.zip 12345
Upper-bound schema
Fernandez, Suciu 1998
16
Schema Extraction(From Data)

• Problem statement
• given data instance D
• find the most specific schema S for D
• In practice S too large, need to relax

S.Nestorov , S.Abiteboul, and R.Motwani,
Inferring structure in semistructure data. In
Proc. of The Workshop on Management of
Semi-structured Data, 1997
17
Schema Extraction(From Data)

• Roy Goldman, Jennifer Widom DataGuides Enabling
  Query Formulation and Optimization in
  Semistructured Databases. VLDB 1997

18
Schema Extraction(From XML Data)

• Minos N. Garofalakis, Aristides Gionis, Rajeev
  Rastogi, S. Seshadri, Kyuseok Shim XTRACT A
  System for Extracting Document Type Descriptors
  from XML Documents. SIGMOD Conference 2000