Conceptual Modeling for XML Data Tok Wang Ling

Conceptual Modeling for XML Data Tok Wang Ling National University of Singapore DASFAA’ 2003 Panel Discussion 1

Outlines • Why do we need conceptual modeling? • What are the important semantic information to be captureｄ? • Uses of conceptual model for some XML research topics 2

Motivation: Why do we need to have a conceptual model to represent XML Data? <department number =“cs”> <name> computer science</name> <course number = “cs 4221”> <name> Database </name> <student number = “ 1234” > <name> B. Y. Smith</name> <grade> 70</grade> </student> <student number=“ 1235”> <name> C. U. Brown </name> <grade> 60</grade> </student> </course> </department> <! ELEMENT department (name, course+)> <! ATTLIST department number ID #REQUIRED> <! ELEMENT course (name, student*)> <! ATTLIST course number ID #REQUIRED> <! ELEMENT student (name, grade? )> <! ATTLIST student number CDATA #REQUIRED> <! ELEMENT name (#PCDATA)> <! ELEMENT grade (#PCDATA)> (b) An XML DTD for (a) XML document 3

▼♦ department Motivation (cont. ) department &1 number cs ♦ number ♦ name ▼ ♦ course ♦ number ♦ name ▼♦ student ♦ number ♦ name ♦ grade (B) Dataguide name course computer science &3 &2 number name student &4 &5 cs 4221 Database number &23 1234 &7 &6 name grade &24 number name student &20 &21 &22 number name grade &25 &26 &27 &28 B. Y. Smith 70 1235 C. U. Brown 60 (a) OEM Diagram Figure 1: Sample instance demonstrating OEM and dataguide 4

Motivation (continue) Q: What are the important semantic information and constraints cannot be captured by the DTD and Dataguide? • What are the object classes? department, course, student? • Attributes of object classes? • Identifiers of object classes? • What are the relationship types defined among object classes? e. g. Relationship types among department, course, student? • What is “grade”? Object class? Attribute of student? • Are there redundancies? 5

Semantic Information to be captured by an XML conceptual model • Object class – attributes of object class – ordering on object class • Relationship Type – – – Represent hierarchical structure degree of n-ary relationship type participation constraints of object classes in relationship type attributes of relationship type disjunctive relationship type recursive relationship type • Reference 6

Semantic Information to be captured by an XML conceptual model (cont. ) • Attribute – key attribute / identifier – composite attribute – disjunctive attribute – attributes with unknown structure – fixed and default values of attribute – derived attribute • Functional dependencies and other constraints • Inheritance hierarchy (class hierarchy) • Semi-structured data instance representation 7

Q: What are the semantic information cannot be represented by Dataguide, DTD, XML Schema? • • • Attribute or object class Degree of relationship type Attibute of object class or relationship type Class hierarchy Functional dependency … 8

A solution: ORA-SS, an object-relationship attribute model for semi-structured data. department Number: CS Name: Computer Science course student Number: Name: CS 4221 Database student Number Name student department 2, 1: n, 1: 1 number: Name: Grade: 1234 B. Y. Smith 70 number: Name: 1235 C. U. Brown Grade: 60 number name course number name Figure 2: ORA-SS instance diagram cs student cs number name grade Figure 3: ORA-SS schema diagram 9

The data model of ORA-SS – – – - Relationship Type attributes of relationship type degree of n-ary relationship type participation constraints of objects in relationship type disjunctive relationship type recursive relationship type project 2, +, + id name project member publication member p 1 2, *, + name job title publication m 1 pub 2 p 3 pub 1 m 2 pub 3 number title (a) ORA-SS Schema Diagram (b) Instance Relationship ▼♦ project ♦ id ♦ name ▼♦ member ♦ name ♦ job title ▼♦ publication ♦ number ♦ title (c) Dataguide Figure 5: Representing binary relationship type 10

The data model of ORA-SS - Relationship Type (cont. ) project id name member p 1 2, +, + p 2 member p 3 m 1 publication pub 1 pub 2 m 2 pub 3 3, *, + name job title publication (b) Instance Relationship ▼♦ project number title (a) ORA-SS Schema Diagram ♦ id ♦ name ▼♦ member ♦ name ♦ job title ▼♦ publication ♦ number ♦ title (c) Dataguide Figure 6: Representing ternary relationship type 11

The data model of ORA-SS – – – - Attribute key attribute composite attribute disjunctive attribute with unknown structure fixed and default values of attribute derived attribute course code title * ANY cs 2, 4: n, 3: 8 student cs dept prefix number D: comp cs * number first last mark grade hobby name Figure 7: Object classes with relationship type and attributes 12 in an ORA-SS schema diagram

Uses of the Conceptual model for XML research • Normal form XML schema – remove redundant data – resolve multiple inheritance conflicts • Storage structure for XML databases – use Object Relational Model • XML Views – – derived information from references and class hierarchy defining views materialized view maintenance view updates • Integration of XML documents • Evaluating XML queries on XML databases 13

Research Topics using ORA-SS Model Normal Form XML Schema • • • Schema may have a lot of redundant data Update anomalies Normal Form schema is needed professor staff# 2 name course 2 C. Code title textbook + ISBN author title 14

Research Topics using ORA-SS Model NF XML Schema (cont. ) • Some better solutions: • Redundancies are removed, in normal form professor staff# name course C. Code course. R course-Ref professor name textbook-Ref title textbook. R + ISBN author title course professor-Ref staff# textbook-Ref C. Code title professor. R textbook. R + ISBN author title 15

Research Topics using ORA-SS Model Storage Structure for XML Databases • Main Rules – Each object class together with its attributes form a nested relation (object relation) – Each relationship type together with its attributes form a nested relation (relationship relation) • Nested relations can be handled by Object Relational model, e. g. ORACLE 8 i. 16

Research Topics using ORA-SS Model Storage Structure for XML Databases Object Relations Supplier S# + Name City SP Part P# Name Supplier (S#, Name, (City)) SP 2 Color Part (P#, Name, color) Price SPJ 3 Relationship relations SP (S#, P#, price) Project SPJ J# Name Loc Project(J#, Name, Loc) Qty SPJ (S#, P#, J#, Qty) Constraint: SPJ[S#, P#] SP[S#, P#] 17

Research Topics using ORA-SS Model XML Views • What information can be directly derived from references and class hierarchy code title course faculty course cs, 2, 4: n, 3: 8 student. R fs, faculty 2, 1: n name student code grade student number cs | * faculty grade history course grade code title student fs cs cs grade student number | hostel home name number street Referencing an object class in an ORA-SS schema diagram hostel name home number street 18

Research Topics using ORA-SS Model XML Views (cont. ) • Valid views of an ORA-SS schema • Operations: selection, projection, join, up/down 2 2 Part 3 2 2 Supplier 2 3 price Project Part Supplier Project Part 2 2 3 Supplier 3 3 3 Qty Qty View 1 View 2 2 total_qty price View 3 19

Conclusion • A good conceptual model is needed for XML database applications: * normal form schema * storage structure * view design and view updates * …. 20