Exporting Databases in XML DTD A Conceptual and Generic Approach

1. Philippe Thiran Computer Science Department Technische Universiteit Eindhoven The Netherlands Exporting Databases in XML DTDA Conceptual and Generic Approach

2. Exporting Databases in XML • Current Situation • XML as the standard for publishing and exchanging data over the Web • Data recorded and maintained in existing Databases • Heterogeneous databases: different data models • Limitation of database models • Database schema incompleteness (implicit/hidden structures) • Explicit and implicit interconnections among entities Oracle V5 Model (no primary and foreign keys)

3. Exporting Databases in XML • Migrating existing databases to XML • Principle • XML description in DTD • Bottom-up Approach • Exploiting as much as possible the meaning of source data • Method and Tool • Method • Not limited to any specific database model • Capturing the explicit and implicit structures and interconnections of the database schema • Tool for supporting the method

4. Exporting Databases in XML Schema Representation Database models and DTD Schema Manipulation Database schemas and DTD

5. Exporting Databases in XML • Schema Representation • Expressing database schemas and XML in terms of GER • Extended object-entity relationship data model • One rich and expressive model able to express data schemas whatever their operational data models • Operational database models like IMS, Relational, OO • XML-family models: XML DTD or XML Schema

6. Exporting Databases in XML • Schema Representation • Expressing XML in terms of GER • DTD expressed in terms of GER • DTD concepts • Hierarchical organization • Sequence organization

7. Exporting Databases in XML • Schema Representation • Expressing XML in terms of GER <!ELEMENT Catalog (Order*, Product*)> <!ELEMENT Order (Customer, Date, Total?, detail+)> <!ATTLIST Order OrderID ID #REQUIRED> <!ELEMENT Customer ANY> <!ELEMENT Date (#PCDATA)> <!ELEMENT Total (#PCDATA)> <!ELEMENT Detail (Quantity, Amount)> <!ATTLIST Detail Product IDREF #REQUIRED> <!ELEMENT Quantity (#PCDATA)> <!ELEMENT Amount (#PCDATA)> <!ELEMENT Product (Supplier+)> <!ATTLIST Product Reference ID #REQUIRED Label CDATA #IMPLIED UnitPrice CDATA #REQUIRED> <!ELEMENT Supplier ANY>

8. Exporting Databases in XML • Schema Manipulation • Transforming XML DTD within GER • Schema transformations defined on GER • Reverse transformations, semantics-preserving transformations • Transformation operators • Standard transformations • For manipulating schemas expressed in operational database models • Example: transforming an entity type into an attribute • DTD-specific transformations

9. Exporting Databases in XML • Schema Manipulation • Transforming XML DTD within GER • Standard transformations • For manipulating schemas expressed in classical structured models • Example of a semantics-preserving transformation: transforming an relationship type into a entity type

10. Exporting Databases in XML • Schema Manipulation • Transforming XML DTD within GER • DTD-specific transformations (example) • Suited to derive a DTD from a structured data schema

11. Exporting Databases in XML Converting (legacy) databases into DTD Exploiting as much as possible the meaning of source data Capturing the explicit and implicit structures and interconnections

12. Exporting Databases in XML • Exporting Databases • Bottom-up approach (from the source to the target) • Semi-automated 4-step method • Extraction of the database schema (automated) • Extraction of the explicit structures and constraints • Semantics recovering (semi-automated) • Recovery of the implicit structures and constraints • Model translation (semi-automated) • Translation of a schema expressed in the GER into a schema expressed in the GER DTD • Use of the relations among entities • DTD exportation (automated) • Generation of the DTD document

13. Exporting Databases in XML • Exporting XML • Reverse Engineering • Recovering of the conceptual schema of an existing database • Augmentation of the knowledge about the data semantics • Database reverse engineering process (DB-MAIN) • Elicitation of hidden structures and constraints Database Schema Conceptual Schema Schema transformations

14. Exporting Databases in XML • Exporting XML • Model Translation • DTD-specific transformation • Non-deterministic process • It requires some design choices • The user-inputs might have consequences on the properties and the semantics of the resulting schema • 5-step transformation process • Schema preparation • Hierarchy structure creation • Constraint relaxation • Attribute representation • Ordering definition

15. Exporting Databases in XML • Schema preparation • Hierarchy structure creation • Constraint relaxation • Attribute representation • Ordering definition • Exporting XML • Model Translation • Schema preparation • Removing invalid constructs • Multivalued/compound attributes • Complex relationship types Conceptual Schema

16. Exporting Databases in XML • Schema preparation • Hierarchy structure creation • Constraint relaxation • Attribute representation • Ordering definition • Exporting XML • Model Translation • Hierarchical structure creation • Entity types, relationship types are transformed into a tree • by electing natural roots (significant concepts) • by resolving father conflicts • by breaking cycles • by (eventually) adding a unique root

17. Exporting Databases in XML • Schema preparation • Hierarchy structure creation • Constraint relaxation • Attribute representation • Ordering definition • Exporting XML • Model Translation • Constraint relaxation • Role cardinalities extension • Gid and idref groups creation

18. Exporting Databases in XML • Schema preparation • Hierarchy structure creation • Constraint relaxation • Attribute representation • Ordering definition • Exporting XML • Model Translation • Attribute representation • Ordering definition

19. Exporting Databases in XML CASE Support – DB-MAIN Model Expression Database models and DTD Model Translation DTD-specific transformation

20. Exporting Databases in XML • CASE Support – DB-MAIN • Basic Features • Dedicated to database application engineering • Based on the GER • Includes transformation operators, reverse engineering processors and schema analysis tools • Extraction facilities (SQL, Codasyl, RPG, IMS, etc.)

21. Exporting Databases in XML • CASE Support • *-to-DTD Transformation • DTD-Specific transformations • Assistant

22. Exporting Databases in XML • Conclusions • Rich and expressive data model • Translating semantics of both database and XML models • Non-deterministic aspect of the model translation • The same database schema can lead to a large set of equivalent XML structures • CASE Support (application) • Automatic production of XML documents • that comply with the DTD that has been computed • based on the schema transformations used to convert the database schema in XML DTD