Datalogand Data Integration Zachary G Ives University of

Datalogand Data Integration Zachary G. Ives University of Pennsylvania CIS 550 – Database & Information Systems November 10, 2005

An Important Set of Questions

Reasoning about Queries and Views

Let’s Go Back a Few Weeks… Domain Relational Calculus

A Similar Logic-Based Language: Datalog

Datalog. Terminology

Datalogin Action

Datalogis Relationally Complete

A Query We Can’t Answer in RA/TRC/DRC… Recall our example of a binary relation for graphs or trees (similar to an XML Edge relation): edge(from, to) If we want to know what nodes are reachable: reachable(F, T, 1) : - edge(F, T) reachable(F, T, 2) : - edge(F, X), edge(X, T) reachable(F, T, 3) : - reachable(F, X, 2), edge(X, T) distance 1 dist. 2 dist. 3 But how about all reachable paths? (Note this was easy in XPath over an XML representation -- //edge)

Recursive. Datalog. Queries

Our Query in RA + while (inflationary semantics, no negation)

A Special Type of Query: Conjunctive Queries

Example of Containment

Wrapping up Datalog …

A Problem

Building a Data Integration System

Typical Data Integration Components

Typical Data Integration Architecture

Challenges of Mapping Schemas

Different Aspects to Mapping Let’s see one influential approach to schema matching…

The LSD (Learning Source Descriptions) System

Example

LSD’s Multi-Strategy Learning

Training the Learners Name Learner

Applying the Learners

Putting It All Together: LSD System Training Phase Matching Phase Mediated schema Source schemas Data listings Training data for base learners L 1 L 2 Lk Domain Constraints User Feedback Constraint Handler Mapping Combination

Mappings between Schemas

A Few Mapping Examples Cust. ID Cust. Name Penn. ID Emp. Name 1234 46732 Smith, J. John Smith

Two Important Approaches

TSIMMIS

XML vs. Object Exchange Model

Queries in TSIMMIS

Query Answering in TSIMMIS

A Wrapper Definition in MSL book title The union of Get. Book’s results is unioned with others to form the view Mediator() author

How to Answer the Query

Query Composition with Views We find all views that define book with author and title, and we compose the query with each: book define function Get. Book($x AS xsd: string) as book { for $b in sql(“Amazon. DB”, author title “select * from book where author=‘” + $x + “’”) return {$b/title} {$x} } for $b in Mediator()/book where $b/title/text() = “DB 2 UDB” and $b/author/text() = “Chamberlin” return $b

Matching View Output to Our Query’s Conditions book title author

The Final Step: Unfolding

Virtues of TSIMMIS

Limitations of TSIMMIS’ Approach