The world of databases been historically has dominated by three great companies (Oracle, Informix and IBM) that offers dedicated products to the management of great amounts of information. These products normally have unattainable prices for an average company and we do not speak of a domestic user. Directed to an average market we found product multitude that can perfectly cover the necessities with any medium company without causing that the budget goes off.
Less known by most of users, several generally developed gratuitous Database managers by Universities or groups of volunteers also exist. Some of these products have a great quality and in many cases they surpass the qualities of his commercial competitors. Between these gratuitous products and of great quality we found to PostgreSQL. The history of PostgreSQL begins like a project of investigation of the group of Professor Michael Stonebraker in Berkeley. Its original project, Ingres, are commercialized at the moment with the same name. The original University Ingres is still available free and uses its own query language ' QUEL'. Its following project was ' Postgres' (post-ingres), that used an advanced query language more: POSTQUEL. In 1987, Postgres introduced definibles rules, procedures, types and concepts of direction to objects. Postgres was commercialized with the name of Illustra and at the moment comprises of the Universal Server de Informix. The original Postgres version 4,2 (still based on POSTQUEL) still can be found by Internet. Two students of the laboratory of Stonebraker, Andrew Yu and Jolly Chen, decided to rewrite great part of the Postgres code and to replace POSTQUEL by an extended subgroup of SQL. This new version was sent in 1995 as Postgres95 and then the development happened to hands of the community of Internet. Postgres95 evolved until which it is now PostgreSQL.
PostgreSQL is a database manager based on the relational model, although it incorporates some concepts of the model OO, such as the inheritance. The USA an extended subgroup of SQL as query language and is implemented following the architecture client-server. PostgreSQL offers great variety of tools and bookstores to accede to Bases de Datos.
In their version 6,3,2 (the last one at the time of writing this document), interfaces for the following languages exist: C. C++. Contracted C. Java (through JDBC). Perl. ODBC (drivers ODBC for PostgreSQL for Windows, Max, UNIX and VMS exist). Python. TCL
Objective
In spite of offering diverse interfaces of programming, PostgreSQL lacks a language of fourth generation (4GL) that facilitates the programming of applications of data bases. With this project it is tried to cover this hollow, developing a compiler for a language 4GL. Tomamos like reference language 4GL of Informix, being the objective for obtaining that programs designed for Informix can recompilados and be used with PostgreSQL with the minimum of modifications.
Informix-4GL offers tools to create menus, forms of entrance of data and generators of listings. It will be necessary to define these same tools maintaining, if possible, the original syntax. In principle applications will be generated that work in way text, leaving for a future extension the generation of applications in graphical surroundings. Objectives that have covered the syntax with the language are almost identical to the one of Informix-4GL.
The basic data types, those of date and hour, intervals and ' datetime have been implemented. The repetitive presentation, assigment statements in screen, structure (curls while and for) and conditional (if..else..), generation of menus and listing have been implemented completely. The handling of the forms of entrance of data has been implemented following the syntax of Informix-4GL original, nevertheless has modified the syntax of the definition of the forms to include to new types of objects, like bellboys or squares of verification. A new sentence has been introduced (browse), that allows to visualize all tuplas given back by a consultation and ' navegar' by them by means of movements of the cursor. The syntax of some sentences has been extended, allowing new functionalities not found in Informix-4GL, like multiple allocations. These modifications are explained with detail in the manual of user. Possibilities of extension an interface has been generated solely in way text.
Nevertheless, the implementation of the functions of handling of entrance forms has been made of independent way of the implentación at low level (you attend). Thanks to this it is possible to develop bookstores of functions that manage the forms of entrance of graphical way, generating interfaces in X-Window. The code generation at the moment is very focused to the interface of PostgreSQL. A possible extension would be the generalization of this code, to even allow the development of applications that accede to data stored in another type of servers, or using ODBC (the API of access to data bases defined by Microsoft and that has become standard).
hy4GL: compiler of language 4GL for PostgreSQL