Functional Dependencies for Object Databases: Motivation and Axiomatization

Object identification by abstract identifiers should be considered as a modeling and not as a database concept. This means that object identifiers are not appropriate for the access to specific objects using a database language. In this paper we discuss how the relational concept of a functional dependency can be adapted to object databases in order to get more convenient ways of accessing objects. Graph based object functional dependencies are proposed as a means to specify constraints between attributes and object types of an object schema. Value based identification criteria can be defined using a special type of object functional dependencies. Different definitions of satisfaction are given for these constraints, based on a so-called validation relation, and their relationships are investigated. These definitions are related to different forms of identification. Using the strongest notion of satisfaction, inference rules for the derivation of new dependencies are discussed with emphasis on the characteristics of rules combining two dependencies, like the transitivity rule. In addition to generalized relational rules further rules are needed, mainly concerned with transition from the object type level to the attribute level and vice versa

Database Migration: A Literature Review and Case Study

This literature review provides an overview of various areas of research in database migration. Specific areas which are addressed are legacy migration, migrating between different database models, reverse engineering, schema design and translation, and security. Additional literature is considered which provides a general overview of the topic. Some case study literature is included with an emphasis on library science studies. This literature review is then applied to a case study migration project at the University of North Carolina at Chapel Hill in order to determine where the literature was helpful and where not, as well as where more research may be needed. Conclusions are drawn that the theoretical literature is quite comprehensive, but that literature having more practical application could certainly be strengthened

View mappings for query languages

The problems of current use of query languages are looked at. One chief drawback is the undesirable requirement for end user familiarity with and knowledge of the underlying database structures, in order to retrieve data effectively. The approach adopted towards resolving this is by means of high-level view support, using unit view structures called perceived records. A prime concern of this thesis then, is the study of perceived record mappings from the database. A set of criteria for categorising and analysing the features of database mappings for end-user views is first developed. In addition, a classification of data structure transformations and data item transformations is also presented. The framework is general and is independent of a specific data model or database management system. Its usefulness is demonstrated by its application to the analysis of view transformations from recursive database structures to high-level, unit view structures. In addition, it serves as a basis for evaluating and comparing the mapping facilities in existing systems. Possible ways of specifying a suitable data model for the perceived record view concept are described. Following on, two general mapping techniques are discussed. This leads to a proposal for a mapping mechanism that supports the flexible derivation of complex perceived record views that can differ considerably from the source structures. The mechanism uses an intermediary canonical transform model. Description of how the transform model mechansim can be used in practical systems to derive perceived record views, is also presented. The feasibility of the ideas proposed are tested out by implementing an interactive software system for defining perceived record views. For this, a mapping definition language for perceived record derivation is first designed. The control system sets up the structures of the mapping definition language and prompts the End-User-Administrator to define and specify the mappings for a perceived record. Appraisals of both the proposed mapping mechanism and implementation are discussed. Examples of use of the interface system are included. The limitations of the implementation are pinpointed with suggestions for further improvements. Practical applications of the work and evaluation of the approach in the light of other existing approaches, are also discussed

Design of relational views over network schemas

An algorithm is presented for designing relational views over network schemas to: (1) support general query and update capability, (2) preserve the information content of the data base and (3) provide independence from its physical organization. The proposed solution is applicable to many existing CCDASYL databases without data or schema conversion. The particular declarations of a CDDASYL schema which supply sources of logical data definition are first identified. Then the view design algorithm is derived on the basis of a formal analysis of the semantic constraints established by these declarations. A new form of data structure diagram is also introduced to visualize these constraints. 1. INTRczaltJcTIm This paper presents a rigorous solution to the problgn of designing relational views &ich support general wery and update capabilities over network schemas. Three objectives are of paramount concern in our approach. They are: 1. information preservation 2. updatability 3. data independence. Let us consider information preservation first. This is needed for supporting general purpose data manipulation capability. Indeed a user must be capable of accessing through views all the information of interest (within his authorization domain). Thus the view must be information-wise equivalent to the underlying schema or that portion of interest. Let us consider now the problem of specifying updates through a view (these include insert delete and modify operations). The simple data organization displayed by a view is often very Permission to copy without fee all or part of this material is granted provided that the copies are not made or distributed for direct commercial ad-vantage, 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 Assooia-tion for Computing Machinery. To copy otherwise, or to republish, requires a fee end/or specific permission