A Generalized Modeling Framework for Schema Versioning Support Fabio Grandi, Federica Mandreoli, Maria Rita Scalas CSITE-CNR, DEIS University of Bologna, Italy The title of my talk is ODMG language extensions for generalized schema versioning support, a work which has been done by myself and Fabio Grandi.

A generalized OODB Model with Schema Versions Support of consolidated and temporal schema versions Support of a complete set of primitive schema changes Provided operational semantics My talk will be articulated in the following points: First I will present a brief overview of the research project to which the present work is one of the contributions, then I will introduce the proposed extension the the ODMG languages for generalized schema versioning support. Finally, I will present conclusions and future work. F. Grandi, F. Mandreoli, M.R. Scalas - ADC 2000

F. Grandi, F. Mandreoli, M.R. Scalas - ADC 2000 The Research Project Extension of the ODMG standard for schema versioning support (branching approach + temporal approach) at level of Object Model ( OODM|SV+ ) Low-level operations (schema changes) High-level language (ODL+OQL) This work has been developed in the framework of a research project whose aim is the extension of the ODMG standard in order to support schema versioning in Object Oriented Databases. The generalized schema versioning we consider includes both temporal schema versioning, as adopted in temporal applications, and branching versioning, usually adopted in design applications. This extension has been partially done at the Object Model level and the outcome is OODM|SV+, which is a model which integrates the pure temporal schema versioning with the branching approach, whereas this paper present the concerned extensions at O D & Q Language level. F. Grandi, F. Mandreoli, M.R. Scalas - ADC 2000

F. Grandi, F. Mandreoli, M.R. Scalas - ADC 2000 Schema Versioning Allows information systems to “survive” after schema re-organizations (schema evolution) Allows legacy applications to continue to work after schema changes are effected Allows to access/modify any available data through any available schema (full schema versioning) F. Grandi, F. Mandreoli, M.R. Scalas - ADC 2000

F. Grandi, F. Mandreoli, M.R. Scalas - ADC 2000 The Branching Approach Early requirements for versioning arose in advanced application domains like CAD/CAM and software engineering Versioning introduced to support different users working on parallel, or even merging, versions of the same piece of data F. Grandi, F. Mandreoli, M.R. Scalas - ADC 2000

F. Grandi, F. Mandreoli, M.R. Scalas - ADC 2000 Branching Schema Versions Schema versioning involves intensional (structural) aspects of data objects Goal: allow a “safe” management of different schemas used at the same time Schema versions organized as a DAG (consolidated / design versions) SV1 SV3 SV4 SV2 F. Grandi, F. Mandreoli, M.R. Scalas - ADC 2000

F. Grandi, F. Mandreoli, M.R. Scalas - ADC 2000 The Temporal Approach Versions have recently shown useful also for other object-oriented applications: GIS Multimedia applications F. Grandi, F. Mandreoli, M.R. Scalas - ADC 2000

F. Grandi, F. Mandreoli, M.R. Scalas - ADC 2000 Temporal Schema Versions Schema versions have a temporal pertinence Allows the management of the history of the structure of data objects Allows the system to keep track of the history of effected schema changes F. Grandi, F. Mandreoli, M.R. Scalas - ADC 2000

F. Grandi, F. Mandreoli, M.R. Scalas - ADC 2000 Temporal Schema Versions Provides a complete support to extant data access by means of past, present and future schema versions Time line SV1 SV2 SV3 SV4 t0 t1 t2 t3 F. Grandi, F. Mandreoli, M.R. Scalas - ADC 2000

A New Integrated Approach A generalized framework for the support of design and temporal schema versions Aimed at improving the application potentialities: full control of the design process in engineering applications concurrent scenario analysis in temporal databases (bifurcation of the time line) F. Grandi, F. Mandreoli, M.R. Scalas - ADC 2000

The Underlying Model: OODM|SV+ A database is a set of versions organized as a DAG Each version has a version coordinate set a bitemporal timestamp a user defined name (label) Versions with the same label belong to the same database node Derivation relationships between nodes are defined by edges In OODM|SV+ a database can be seen as a set of versions organized as a DAG. Each version is made up of a schema version and the corresponding data pool and is referenced thought a set of version coordinates that is a a bitemporal timestamp for temporal schema verisoning support and/or a user defined name, named label, for branching versioning support. All versions with the same label share a common property and, for this reason, belong to the same node. Derivation relationships between nodes are defined with edges in the DAG. F. Grandi, F. Mandreoli, M.R. Scalas - ADC 2000

F. Grandi, F. Mandreoli, M.R. Scalas - ADC 2000 Basic Components Time represented as: TIME={0,1,…,now,…,} bitemporal domain: TIMEt TIMEv Temporal version: TV=(SV,SDV) representing a homogeneous state of the world with a unique time pertinence Schema Version (SV): intensional component Stored Data Version (SDV): a consistent instance set F. Grandi, F. Mandreoli, M.R. Scalas - ADC 2000

F. Grandi, F. Mandreoli, M.R. Scalas - ADC 2000 The Database Concept A database is a function DB: (L  TIMEt TIMEv) TVS {} It associates one temporal version to each time-point and label vt TV1 TV2 tt L1 vt vt TV1 TV1 tt tt vt tt TV2 TV1 L4 L3 L2 F. Grandi, F. Mandreoli, M.R. Scalas - ADC 2000

Schema Change Primitives The set of schema change primitives allows non-destructive changes to consolidated versions allows the generation of a new consolidated version (DAG node) allows the integration of features of different consolidated versions allows the addition of a new semantic derivation (DAG edge) F. Grandi, F. Mandreoli, M.R. Scalas - ADC 2000

The Taxonomy of Primitives Modifications acting on nodes: on attributes, relationships, operations and exceptions on hierarchical relationships on the type collection Modifications acting on edges: pick-, new- and merge-type F. Grandi, F. Mandreoli, M.R. Scalas - ADC 2000

Semantics of Primitives (1) Starting from: a schema change u two version identifiers ss1, ss2L TIMEv a schema change validity sc ss1 ss2 TV1 TV2 L1 L1 u TV sc L1 F. Grandi, F. Mandreoli, M.R. Scalas - ADC 2000

Semantics of Primitives (2) The TVU function: generates a new TV by applying u to the selected TVi The BDBU function: selects the TVi identified by ssi places the new TV in the database with the assigned validity sc ss1 ss2 TV1 TV2 L1 L1 u TV sc L1 F. Grandi, F. Mandreoli, M.R. Scalas - ADC 2000

Conclusions and Future Work we proposed a new generalized model for the management of schema versions in OODBMS with a complete set of schema changes Future Work study of semantic and implementation issues addition of other versioning dimensions (e.g. space) We have proposed and ODL/OQL extension for generalized versioning support. Our future work will be devoted to the definition of a detailed semantics for the proposed language extensions based on the underlying model the addition of other versioning dimensions like spatial ones. F. Grandi, F. Mandreoli, M.R. Scalas - ADC 2000