O2, an object-oriented data model

Abstract

A b stractT h e Altdir group is currently designing an objectorien ted d ata base sy stem called 0 2 T h is paper presents a form al description of the ob ject-orien ted d ata m odel of th is system . It proposes a typ e system defined in the fram ework of a set-an d -tu p le d a ta m odel. It m odels the w ell know n inheritance m echanism and enforces strong typing. IntroductionOne of the o b jectiv es of th e Altdir G roup is to develop a new gen eration d atab ase system . T h e targ et app lication s are tradition al b u sin ess app lication s, transaction al appli cations (exclu d in g very high perform ance applications), office au tom ation and m u lti-m ed ia applications. T he sy stem w e are d esigning is object-oriented. W e briefly recall th e m ain featu res of th e object-oriented paradigm : (i) O b ject id en tity. O b jects h ave an existen ce w hich is in d ep en d en t of their value. T hus, tw o ob jects can be either id entical, th a t is, th ey are th e sam e object, or th ey can be equal, i.e., th ey have th e sam e value. (ii) T h e n otion of type1. A typ e describes a set of ob jects w ith th e sam e characteristics. It describes the struc ture of d a ta carried b y ob jects as w ell as th e opera tio n s (methods in th e ob ject-orien ted term inology) applied to th ese objects. U sers of a typ e only see the in terface of th e typ e, th a t is, a list of m eth odsPermission to copy without fee all or part of this material is granted provided that the copies are not made or distributed for direct com mercial advantage, the ACM copyright notice and the title of the publication and its date appear, and notice is given that copying is by permission of the Association for Computing Machinery. To copy otherwise, or to republish, requires a fee and/or specific permission. © 1988 A C M 0 -8 9 7 9 1 -2 6 8 -3 /8 8 /0 0 0 6 /0 4 2 4 $1.50 togeth er w ith their sign atu res (th e typ e of the input param eters and the typ e of the result): th is is called

Incremental inheritance model for an OODBMS

“…In OODBMS, there are several solutions to such ambiguities. In the 02 [21], the system solves the name conflict by renaming the conflicting properties. Furthermore, intervention from the user is required to solve some conflicting cases [2].…”

“…if x:t' of C' has been redefined in C with x:t, therefore t _<st t' for the attribute x. If x is a method, where t'= sign(x) in C' and t= sign(x) in C, therefore t <~_m t' [21]. Thus T(GC) ~ T(GC').…”

“…This problem is caused by the interaction between recursion and subtyping [1,3,13]. C. Lecluse and P. Richard et F.Velez [21] use "covariance specialization" (~ > 13 < o/ ~ ~r iff a < c~' and ~ < ~')) as the subtyping rule for method types in the O2 DBMS. This approach gives a less restrictive type system, but is safe [21], more natural, flexible and expressive [11].…”

“…C. Lecluse and P. Richard et F.Velez [21] use "covariance specialization" (~ > 13 < o/ ~ ~r iff a < c~' and ~ < ~')) as the subtyping rule for method types in the O2 DBMS. This approach gives a less restrictive type system, but is safe [21], more natural, flexible and expressive [11]. We show that the proposed model respects the Cook's constraint, when we use the subtyping relation (<) defined in the O2 DBMS.…”

A spatial data model underlying human interaction with object-oriented spatial databases

“…Our model might be comparable to semantic data models, such as [ll]. for the part concerning the general abstraction primitives (i.e., classification, generalization, and aggregation) and to 00 data models, such as [24,14,3,16,18]), for the presence of methods, although these models have as the first goal the conceptual design of a general database schema. For the part concerning the spatial primitives (topological and metric relationships), our model seems to be similar to works in the area of GISs, such as [9, 23, 51, even though these works look at spatial relationships from the point of view of geographic data processing and physical data structures.…”