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Despite the many advances that have been made in the field of database management in the last two decades, in many respects the paradigm of database management has not changed much since its inception. Several long-standing assumptions pervade the field and exert a great influence on the architecture of database management systems, their functions, and. the kinds of databases that they manage. This paper reconsiders some of these assumptions and suggests certain alternatives to them. In particular, it is argued that the concept of an integrated database ought to be supplanted by that of a federated database, a loose assembly of semi-independent components; the position of the database management system in the context of a total information system is reexamined, and arguments are made for extending its functional capabilities; and controlled logical redundancy in the schema is introduced as a means of improving the usability of a database and of enhancing its life-cycle performance. An underlying theme throughout is that of the importance of a semantic schema of the database, which specifies enough of the meaning of the application domain to enable enhanced functionality to be achieved. A number of characteristics of a conceptual data model (in which this scheme would be expressed) are described.

The "semantic integrity" of a data base is said to be violated when the data base ceases to represent a legitimate configuration of the application environment it is intended to model. In the context of the relational data model, it is possible to identify multiple levels of semantic integrity information: (1) the description of the domains of the data base, as abstract sets of atomic data values (domain definition), (2) the specification of the fundamental structure of the data (relation structure specification), (3) the definition of the abstract operations which are meaningful in terms of the application environment (structured operations), and (4) the expression of additional semantic information not contained in the structure of the relations nor in the identities of their underlying domains (relation constraints).

Popular content management systems such as WordPress and Drupal offer a plug-in mechanism that allows users to extend the platform with additional functionality. However, plug-ins are typically isolated extensions defining their own data structures, application logic and user interface, and are difficult to combine. We address the fact that users may want to configure their applications more freely through the composition of such extensions. We present an approach and model for component-based web engineering based on the concept of components and connectors between them, supporting composition at the level of the schema and data, the application logic and the user interface. We show how our approach can be used to integrate component-based web engineering into platforms such as WordPress. We demonstrate the benefits of the approach by presenting a composition plug-in that showcases component composition through configurable connectors based on an eCommerce application scenario.

We introduce CompIS, an approach, model and platform for model-driven component-based information system engineering. Our Approach is based on the concept of shared components and connectors between them. To address the data-intensive nature of information systems, our components follow an extended model-view-control structure that also includes data. Component composition is based on configurable connectors, which define the collaboration logic between components and support component composition at the level of the component model, view, control and data. The CompIS UML profile allows to graphically define new components, connectors and compositions. The CompIS platform is a model-driven engineering environment, based on an Extended object database that natively integrates the CompIS model. From graphical UML model definitions, the platform automatically generates application code that creates and initialises components and connectors. We present and validate our approach in the eCommerce domain.

Today, web development platforms often follow a modular architecture that enables platform extension. Popular web development frameworks such as Ruby on Rails and Symfony, as well as content management systems (CMS) such as WordPress and Drupal offer extension mechanisms that allow the platform core to be extended with additional functionality. However, such extensions are typically isolated units defining their own data structures, application logic and user interfaces, and are difficult to combine. We address the fact that applications need to be configured more freely through the composition of such extensions. We present an approach and model for component-based web engineering based on the concept of components and connectors between them, supporting composition at the level of the schema and data, the application logic and the user interface. We have realised our approach in two popular web development settings. First, we demonstrate how our approach can be integrated into web development frameworks, thus bringing component-based web engineering to the developer. Second, we present, based on the example of WordPress, how advanced end-users can be supported in component-based web engineering by integrating our approach into CMS. The applicability of our approach in both settings demonstrates its generality.

Changes to the conceptual structure (meta-data) of a database are common in many application environments and are in general inadequately supported by existing database systems. An approach to supporting such meta-data evolution in a simple, extensible, object database environment is presented. Machine learning techniques are the basis for a cooperative user/system database design and evolution methodology. An experimental end-user database evolution tool based on this approach has been designed and implemented.

An important issue to be addressed in supporting information sharing in federated database systems is the management of the inherent interdependencies among data in different databases. In particular, data in such databases can (implicitly and/or explicitly) exhibit various forms of interdependence, such as existence, structural, and functional/behavioral dependencies. The ability to capture and systematically support such intrinsic interdependency relationships is essential. In this paper we analyze these interdependencies in the context of an object-oriented database federation, and describe how object-oriented concepts and mechanisms can be employed to accommodate them.

This annual technical report summarizes accomplishments and progress of thirteen (13) work units (projects) for research performed during the reporting period under the Joint Services Electronics Program by the University of Southern California Electronic Sciences Laboratory.

Despite the many advances that have been made in the field of database management in the last two decades, in many respects the paradigm of database management has not changed much since its inception. Several long-standing assumptions pervade the field and exert a great influence on the architecture of database management systems, their functions, and the kinds of databases that they manage. This paper reconsiders some of these assumptions and suggests certain alternatives to them. In particular, it is argued that the concept of an integrated database ought to be supplanted by that of a federated database, a loose assembly of semi-independent components; the position of the database management system in the context of a total information system is reexamined, and arguments are made for extending its functional capabilities; and controlled logical redundancy in the schema is introduced as a means of improving the usability of a database and of enhancing its life-cycle performance., Prepared in cooperation with the University of Southern California, Los Angeles, Dept. of Computer Science.

The conventional approaches to the structuring of data bases provided in contemporary data base management systems are in many ways unsatisfactory for modelling data base application environments. The features they provide are too low-level, computer-oriented, are representational to allow the semantics of a data base to be directly expressed in its structure. The semantic data model (SDM) has been designed as a natural application modelling mechanism that can capture and express the structure of an application environment. The features of the SDM correspond to the principal intentional structures naturally occurring in contemporary data base applications. The SDM provides a rich but limited vocabulary of data structure types and primitive operations, striking a balance between semantic expressibility and the control of complexity. Furthermore, facilities for expressing derived (conceptually redundant) information are an essential part of the SDM; derived information is as prominent in the description of an SDM data base as is primitive data. The SDM is designed to enhance the effectiveness and usability of data base systems. There are many data base management systems in use today which represent a considerable investment on the parts of their developers and users; the SDM can be effectively used in conjunction with these existing data base systems to enhance their effectiveness and usability.

The 'semantic integrity' of a data base is said to be violated when the data base ceases to represent a legitimate configuration of the application environment it is intended to model. In the context of the relational data model, it is possible to identify multiple levels of semantic integrity information: (1) the description of the domains of the data base as abstract sets of atomic data values (domain definition), (2) the specification of the fundamental structure of the relations of the data base (relation structure specification), (3) the definition of the abstract operations which are meaningful in terms of the application environment (structured operations), and (4) the expression of additional semantic information not contained in the structure of the relations nor in the identities of their underlying domains (relation constraints). A high level, nonprocedural domain definition language facilitates the description of domains. Such a language allows the specification of the properties of the values constituting a domain, and the action that is to occur if an attempt is made to update a column entry such that it does not belong to the underlying domain of that column. The specification of relation structure and structured operations can be accomplished by means of high level integrity (sub)languages. A semantic integrity subsystem (of a generalized relational data base management system) can support the generation and maintenance of integrity specifications, verify that these specifications are met by the data base, and take appropriate action if violations are detected.