1 Spring 2000 Christophides Vassilis ODBMS: PROTOTYPES & PRODUCTS l Systems providing object databases programming languages Prototypes: Encore-Ob/Server

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Spring 2000

Christophides Vassilis

ODBMS: PROTOTYPES & PRODUCTS

Systems providing object databases programming languages Prototypes: Encore-Ob/Server (Brown Univ.), IRIS (Hewlett-

Packard), EXODUS (Winsconsin Univ.), Zeitgeist (Texas Instrument), Orion (MCC), ODE (Bell Lab), Gbase (Graphael), Vodak (GMD), TI Open OODB (Texas Instrument)

Products: GemStone (Serviologic), ObjectStore (Object Design), ONTOS (Ontologic), Versant (Versant Object Tech.), O2 (Ardent Software), Objectivity/DB (Objectivity), POET (Poet Software), Jasmine ii (Computer Associates Inter.)

Object Extensions of Relational DBMS Illustra (Illustra Technologies), UniSQL (UniSQL Inc.), OpenODB

(Hewlett- Packard), Matisse (ABC), Omniscience (Omniscience), Polyhedra (Polyhedra PLC), PostgreSQL (PostgreSQL Organization)

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The ODBMS Manifesto [M.Atkinson & al 89]

ODBMS

DBMS OPL

PersistenceDisk ManagementConcurrencyRecoveryAd hoc Queries

DistributionLong TransactionsVersions

Complex objectsObject IdEncapsulationTypes or ClassesSimple inheritanceOverloading & Late bindingComputational Completeness

Multiple inheritancePolymorphism, Genericity

Open Choices: Uniformity of the Model (Classes/Methods/Objects) Naming and Persistence Model Typing System (Classes and/or Types)

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Uniformity of the Data Model

Three independent choices: At the implementation level: are classes and methods represented

as objects? At the language level: are classes and methods treated as objects

(syntactical and semantic uniformity)? At the interface level: are classes and methods presented as

objects? Unlike O2 and ONTOS, in Orion, Gemstone and IRIS the classes are

objects

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Towards Persistence Modeling

How objects become persistent (i.e., database objects): two approaches Persistence is defined independently from the language: it is a property

of the data model (using names) By class names: classes instances are automatically persistent (e.g.,

ORION) By persistent root names: each object referenced by a root becomes

persistent (e.g., O2) Persistence is a property of the underlying language

By library classes provided by the system: objects becomes persistent if there classes inherit from a specific class Object (Ontos) or PObject in (Versant)

By an expression of the language: e.g., persistent (Object Store), persist (Zeitgeist) pnew and pdelete (ODE)

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Aspects of Persistence

Orthogonality of persistence and types: data can be persistent independently of its type

Instances of types can be persistent or transient (e.g., O2, ObjectStore)

Orthogonality of persistence and objects creation: definition and methods for memory allocation are the same for persistent or transient objects

There is not a need to copy objects from the program work space to the database in order to make objects persistent (O2)

Behavioral transparency: uniform manipulation of persistent or transient objects in programs

No distinction in access and update operations nor in variable declarations

Persistence is a property which can be attached either to types or instances: two paradigms of persistence propagation

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Persistence Propagation by Inheritance

Root Class of Persistence: PObject All subclasses of persistent

classes became persistent New and Delete messages are

overloaded A Lookup primitive is added for

searching Non orthogonal to types

Only the types which inherit from PObject persist

Duplication of persistent and transient classes

PobjectNew

DeleteLookup

PPerson NameBorn

…

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Persistence Propagation by Reference

Definition by the programmer of Persistent Roots Keyword ”database" or ”persist" added:

Artist* art = new database Artist( "Monet"); Persistence objects are catalogued

accessible by a Lookup method

All objects referenced by a persistent object become persistent References become persistent during object

storage references are replaced by oids

Dictionary

San Diego Museum of Art

Haystacks

Monet

Monet

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Object Deletion: DB vs. PL view

DB Approach: Explicit “delete” operation Dangling references can be managed

automatically or by the user PL Approach: Implicit deletion when

objects are not any more referenced by others

The difficult deletion of individual objects implies the use garbage collector techniques

att1 X?

att1 X

obj1 obj2

obj1

Garbage Collected

obj2

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The Issue of Naming in ODBMS

Naming and Persistence in ODBMS are closely related

Names specify how to enter the database graph

Impact of the naming model on the simplicity and expressiveness of the QL

Two naming approaches: Implicit => query only the class

extensions i.e., set of instances Explicit => query any object or

value in the database NOTE: In the relational model only

the relations are named and the queries are on collections of tuples

Persistent RootsNames

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Typing System: Object/Class vs. Value/Type

An object is encapsulated in a class

(structure & behavior) is manipulated by methods

(encapsulation) has an identifier (data sharing)

A value has a type (just a structure no

methods) is manipulated by functions (no

encapsulation) hasn’t an identifier

A Compromise: Imperative vs. Object-Oriented Two paradigms: All Object and Object/Value ODBMS

Types are used for documentation correctness (type checking) efficiency (optimization)

Classes add object factory (new) object behavior (method

implementation) collection (extent)

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A Compromise

All Object DBMS Structuring primitives are objects (e.g., collection classes) Meta-Classes & Inheritance at class level Class extensions are managed by the system Possible explicit object deletion Example: GemStone Provides for complex behaviors

Object/Value DBMS Structuring primitives using type constructors Inheritance defined by sub-typing Class extensions can be managed by the programmer Object deletion using a Garbage Collector Example: O2 Provides for complex structures

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LANGUAGE-ORIENTED SYSTEMS Decrease the distance between the type system (data model) of

the PL and that of the database (e.g., ONTOS) SYSTEMS WITH PERSISTANT PL

In addition to the reduction of the impedance mismatch between the PL and the DB the frontier between the language and the database disappears (e.g., ObjectStore, ODE, Zeitgeist, Versant)

APPLICATION-ORIENTED SYSTEMS Providing functionality suited to specific applications for example

(CAD, CAM, CAE) versions, schema evolution, long transactions, etc. (e.g., Objectivity)

COMPLETE ODBMS Integrate the functionality of a DBMS with the object-oriented

technology (e.g., GemStone, O2)

A Classification of the Systems

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DBMS: A Complex and Evolving World

Copyright© 1997 Poet Software

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VIII) REFERENCES M. J. Carey and D. J. DeWitt: “Of Objects and Databases: A Decade of

Turmoil”. In Proc. of VLDB’96, pp. 3-14, Bombay, India, Sept. 1996 M. Atkinson, F. Bancilhon, D. DeWitt, K. Dittrich, D. Maier and S. Zdonik:

“The Object-Oriented Database System Manifesto”. In Proc. of the DOOD’89, pp. 223-40, Kyoto, Japan, Dec. 1989

R. Brachman: “What IS-A is and Isn't: An Analysis of Taxonomic Links in Semantic Networks”. IEEE Computer. 16(10). pp. 30-36, Oct, 1983.

G. McFarland, A. Rudmik, and D. Lange: “Object-Oriented Database Management Systems Revisited”, Modus Operandi, Inc. 1999

F. Manola: “An evaluation of Object-Oriented DBMS Developments” Technical Report GTE Labs, 1994

F. Bancilhon,C. Delobel,S. Gamerman:“SGBD Orientés-Objet”, GIP Altair M. Scholl: “Les SGBD Orientés-Objet”. Course Slides, CNAM Paris B. Amann: “Des SGBD Relationnels aux SGBD Orientés-Objet”. Course

Slides, CNAM Puteaux Y. Viémon: “Object-Orientation and Databases”. Course Slides, PARIS-VI G. Gardarin: “Bases de Données - Relationnel et Objet”. Course Slides,

Université de Versailles Saint-Quentin-en-Yvelines

Documents

1 Spring 2000 Christophides Vassilis ODBMS: PROTOTYPES & PRODUCTS l Systems providing object databases programming languages Prototypes: Encore-Ob/Server