Towards a Formal Approach for Object Database Design P. Poncelet M. Teisseire R. Cicchetti L. Lakhal University of Nice-Sophia Digital Equipment IUT Aix-en-Provence ESSTIN Antipolis Ferney Voltaire University of Aix-Marseille II University of Nancy I 13s - CNRS - URA 1376- 250 avenueA. EinsteinSophia Antipolis - 06560 Valbonne- FRANCE E-mail: [email protected] Tel: (33) 92 94 26 22 - Fax: (33) 92 94 28 98 Abstract 1 Introduction This paper focuseson a formal approach* for advanced Modeling needs for new applications and flaws in the databasemodeling and design. It is based on the IF02 relational model have led to the definition of more model,an extensionof the semanticmodel IF0 definedby powerful mod& which are extended relational [I] or S. Abiteboul and R. Hull. It preserves the acquired object-oriented [5], [6] and [15]. The generic term for strengthsof the semanticapproaches, whilst integrating associated systems, of which certain prototypes are concepts of the object paradigm. To model an IF02 described in [26], is Advanced DatabaseManagement schema,the structuralpart of the modelincluding concepts Systems.As a consequence,current research work is such as alternative, composition, grouping for building focusing on the definition of new modcling and design complex objects and semantic constraints is formally approachesable to satisfythe needsof both traditionaland specified.Furthermore, the definitions of updatefacilities advancedapplications [7], [l l] and 1131.The prcscntcd necessary to modify and perfect IF02 schemas are researchwork fits into this context:a new approachwhose specifiedthrough changerules. Finally, in order to design threemain aspectsare the following ones.Firstly, a formal a databaseschema, an IF02 schemais translated,in an object model IF02 1281is defined for advanceddatabase automaticalway, into an existing target (implementable) modeling as an extension of the semantic model IF0 model.As an illustration,we presenta translationfrom the proposedby S. Abiteboul and R. Hull [2]. Its objective is IF02 model into the CQone. The result is a new coherent actually to reconcileapparently opposed ideas: an optimal and formal approachwhich is useful in overcomingsome data representationand a completereal world modcling. of the difficulties in the specificationand designof object- IF02 attempts to preserve the acquired strengths of orientedapplications. semanticapproaches. whilst integrating conceptsof the object paradigm [4]. Secondly, structural update primitivesarc formally proposedthrough change functions to offer an incrementalspecification of IF02 schcmas. They are crucial for they assistthe designer to take into account real world evolutions or to rectify a part of his schemawithout redefining the whole. They also play a * Thix wok. xuppod by the PRC-BD3 and WI Extawl Euntpean Rorslmh part in the merging of existing sub-schcmasand so they hjxol in coR&0doo with Digital Bquipnau, amnoawilbin Ih uq4 of a larger may be seen as one important element in a vicw- pmjsct whas aim is to realize m aided system for l dvumcd rppliutioo modeling integration process. Finally, in order to design object and dcsip. databaseschema, a set of transformationrules translates Permission to copy without fee all or part of this material is an IF02 schemainto an implementableone granted provided that the copies are not made or distributed far direct commercial advantage.the VLDB copyright notice and fhe The aim of this paper is to describe our approach in title of the publication and its date appear, and notice is given conuastwith the relatedworks and particularyto present: that copying is by permission of the Very Large Data Base 1. The structuralpart of the IF@ model. Endowment.‘To copy otherwise, or to republish, requires a fee 2. The associatedstructural update facilities through an&or special permissionfrom the Endowment. changerules. Proceedings of the 19th VLDB Conference, 3. The formalization of the translation rules from an Dublin, Ireland, 1993. IF02 schema to an 02 one (according to the 278 cstablishcd02 model [ 161)to justify (and illustrate) modelobjective is to integratethe object paradigmwhilst our approach. retaining IF0 modeling strengths. It boosts modeling Finally, we briefly give some aspects of the abilities and appears more suitable for advanced implementationof the system. applicationdesign than object models. To modify and perfect an IF02 schema,formal structural updatefacilities are offered. Thesechanges are formally takeninto considerationthrough updatefunctions [23]. 2 Related Works and Proposal Whenthe schemaseems to be completefor the designer,it would be carried out, automatically,into a target model, Before presentingour approachand in order to highlight by usinga transformationfunction. its contributions,it would be interestingto providea brief surveyof modelingand designapproaches. Among them, We assert that it is essential to have a really rigorous therearc two main trends. approach as IF02 The object paradigm allows and The fit group involvessemantic currents. They are based encouragesa modular modeling of the real world. So, on conceptual(or semantic)mod& for real representation. object modeling can sometimeslook “anarchistic” and Their principle is to offer the users concepts powerful thereforedifficult to handle 1311.In order to avoid such enoughto achieve,from the real world, the mostcomplete problems,a formal approachleads to a schemawhich is specification possible. The resulting schema is then non-ambiguous,without omissions,modifiable and easily translatedinto a logical or implementableone. We may reusable.Moreover, it has the advantageof faciliting not quote [Ill, [17], 1271and [301. However, the classical only the comparison of different designs but also the models in this group generally suffer from the lack of verification of updateson specificationswithout further concepls (object-identity, reusability,...) which are validations. efficient for advancedapplication modeling. Furthermore, in this trend, structuralupdating capacities are not always First of all, we presentthe IFO;! model. Update facilities proposed,and when they exist, they are describedin an are thenexplained and definedthrough change rules. intuitive way. The second class encompassesobject-oriented currents. Their major goal is to capture the dynamic aspectsof applications[21] and [25]. In contrastwith the fit class, 3 The IF02 Model &se approachesdo not offer enoughstructural concepts (often limited to those of implementableobject mod&) IF02 adopts the philosophy of the semanticmodel IFO. for a completereal world modeling.Generally, additional Two main extensionsare realized. Firstly, an explicite methods are used to express semantic structural definition of the object identifier which is object value constraints,These trends do not respectthe indcpendcnce independent, is integrated. To achieve this, all betweenthe sourceand target models.Furthermore, they manipulatedelements of IF0 are re-defined to consider involve an optimized representationof data, i.e. type- the object paradigm. Secondly, to fully meet our oriented,when an attribute-orientedmodeling is advisable “conceptual”objectives, the modelingpower of IF0 must for the conceptual level [13]. The implication for the be enhanced. Then, the concepts of alternative, database designer is the necessity of specifying composition and grouping for building complex objects preliminary representation choices. These choices have been intcgratcd. The connectivity and existency sometimescut off partsof the real world being modelled. constraintsare explicilly specified. The object models provide database evolution In the next sections, we propose a part of formal mechanisms(three trends have been defined in [3]) but definitions of the IF02 model. Instance and attached they do not deal with conceptual schemas,and their object conceptsare not presented,the interestedreader can objectivesdiffer from ours. However,they are interesting rcfcr to [28]. Firstly, the object and type conceptsare for they pinpoint two levelsto be takeninto consideration: dcscribcd as well as the different constructors. The the IS-A hierarchy and the composition hierarchy. For fragmentnotion and IF02 schemaare thendetailled. instance, we may quote: the Mosaic0 system where algorithms are defined for type insertions into a lattice [ 191;the Esseproject where algorithmsensure consistent 3.1 Object and Type updatesof an 02 databaseschema 191 [32]; the Gemstone In the IFOZ,model, an object hasa uniqueidentifier which [22] and Orion [ 141systems, the Sherpa[201, Farandole2 is indcpcndantof its value. Furthermore,the domain of a [3] and Cocoon [29] projects:where rules for the schema type describes the possible values for its objects. The evolutionare stated. figure I showsthe componentsof the type ‘Name’. We would suggestan approachbased on the formal model IF02 which is both type and attribute oriented.The IFO;! 279 Object Type Type Domain 3.1.2 Complex Types The IF02 model takesinto accountfive type constructors \ \ String [20] and makesa distinction betweenan exclusiveand a non- Name exclusivebuilding. Theseconstructors may be recursively 0~7 (id N1. ‘JOCELYN’)~=(tdN2,‘HUGO’) ’ applied according to specified rules for building more complextypes. For example(see the figure 3). ‘Address’is built up from Objects of Type ‘Street’, ‘Number’ and ‘Zipcode’ types and ‘Wheels’ is Figure 1 - Object Type Example composedwith the ‘Wheel’type obtained from ‘Axle’ and Tyre’ tyt?es. Defidlion 1: 70 is