We describe a framework to support the implementation of web-based systems intended to manipulate data stored in relational databases. Since the conceptual model of a relational database is often specified as an entity-relationship (ER) model, we propose to use the ER model to generate a complete implementation in the declarative programming language Curry. This implementation contains operations to create and manipulate entities of the data model, supports authentication, authorization, session handling, and the composition of individual operations to user processes. Furthermore, the implementation ensures the consistency of the database w.r.t. the data dependencies specified in the ER model, i.e., updates initiated by the user cannot lead to an inconsistent state of the database. In order to generate a high-level declarative implementation that can be easily adapted to individual customer requirements, the framework exploits previous works on declarative database programming and web user interface construction in Curry.
The iData toolkit @cite_4 is a framework, implemented with generic programming techniques in the functional language Clean, to construct type-safe web interfaces to data that can be persistently stored. In contrast to our framework, the construction of an application is done by the programmer who defines the various iData elements, where we generate the necessary code from an ER description. Hence, integrity constraints expressed in the ER description are automatically checked in contrast to the iData toolkit.
@cite_4
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In this paper we present the iData Toolkit. It allows programmers to create interactive, dynamic web applications with state on a high level of abstraction. The key element of this toolkit is the iData element. An iData element can be regarded as a self-contained object that stores values of a specified type. Generic programming techniques enable the automatic generation of HTML-forms from these types. These forms can be plugged into the web application. The iData elements can be interconnected. Complicated form dependencies can be defined in a pure functional, type safe, declarative programming style. This liberates the programmer from lots of low-level HTML programming and form handling. We illustrate the descriptive power of the toolkit by means of a small, yet complicated example: a project administration. The iData Toolkit is an excellent demonstration of the expressive power of modern generic (poly-typical) programming techniques.