For many years, the only means of accessing information stored in databases were through interactive SQL interpreters or purpose-written application programs. Such programs could be written in conventional programming languages with the data access components provided by 'Embedded SQL', or in special-purpose database programming languages. One class of these languages, known as 4th Generation Languages (4GL), became popular for rapid application development.
Most 4GLs were based around data-entry and presentation forms with menu choices to move between forms and invoke various operations. In many cases simple data maintenance programs can be generated entirely by an interactive process of selecting required component; writing program code only being necessary to add specialised functionality. However, most 4GLs had a major limitation, a lack of compatibility with each other. Although a few have been designed to be more general, most were supplied as part of a DBMS installation and were specific to the particular vendor's product.
Embedded SQL also suffered from vendor-specific implementations. One approach to overcoming this compatibility problem was to separate applications from their database access components. Particularly successful in this respect was the introduction of ODBC by Microsoft. ODBC is an implementation of the previously little used SQL Standard 'Call Level Interface' (CLI). Using ODBC, programmers could write one program that could access any DBMS, provided that a suitable driver module was available to provide connectivity between program and database. Many generic 4GLs and other database interfaces have been developed using this approach.
The growth of the Internet has had a significant impact on both the use of databases and on methods by which information can be accessed. Previously, databases were mostly used for in-house applications within organisations. Here, incompatibility was rarely a problem unless the organisation decided to change its DBMS or merged with another that used a different system. Specialised software — applications, 4GL or connectivity libraries — needed to be installed on each machine within the organisation and, if access was required by outside or remote users, they too would need to install these special components. With proprietary software this usually had costly licensing implications.
With widening access to the World Wide Web and the ubiquity of HTML browsers, it soon became apparent that databases could be used to provide public access to stored information, and to support such ventures as direct online shopping. The impact on archaeological information has been no less significant. Many systems providing access to online site reports, data archives (Richards, this volume), and local and national monuments registers (Gilman, this volume; Murray, this volume) now depend on HTML form interfaces and a variety of techniques for user-interaction and delivery of information.
The use of browsers and web forms has now effectively supplanted earlier use of 4GLs. Today, very few designers would choose to use one of the older methods where their needs can be satisfied by something that can run in a normal web browser. However, there is an ever-growing profusion of techniques that can be used to deliver database applications over the Internet or an Intranet. The next section provides an outline of the most important approaches.
© Internet Archaeology
Last updated: Wed 28 Jan 2004