A deductive object - oriented approach to Geographic Information Systems
5 The GIS Data Manipulation Language
The four major data manipulation language commands are:
6 Examples of the Language
A Prototype
A prototype of the GIS model proposed has been developed on an MS-DOS microcomputer using Smalltalk/v. As an object-oriented programming language, Smalltalk/v provides the user with facilities objects, classes and methods. It also has, as a class, a logic programming language called prolog/v. Therefore, Smalltalk/v is ideal for the development of the prototype. The developed prototype consists of two major subsystems: user interface and class hierarchy.
1 User Interface
The user interface subsystem is carried out via windows. There are three types of windows provided by the system: GIS Class Hierarchy Browser, GIS Rule Browser, and GIS Query Browser.
The GIS Class Hierarchy Browser allows the user to create new classes or delete existing ones. When the user creates a new class, its definition will be stored in the system dictionary and if there the system dictionary and if there is no inconsistency with the is no inconsistency with the existing classes or objects, it will be inserted into the extensional database.
The GIS Rule Browser helps the user to insert new rules or delete existing one. When the user inserts and new rule, the system checks wheather the new rule is valid or not. If it is valid, then it will be stored in the intensional database.
The GIS Query Browser enables the user to ask questions and obtaine dinformation by suing a set of extended SQL commands described in the previous section. This browser also provides a graphic pane to display data in geometric views.
2 Class Hierarchy
The prototype assumes that there are six object classes: Magnitude (for primitive objects), Collection (for the formation of complex objects), GeoObject, Logic (for Prolog/v), Class Hierarchy Browser (for browsing and editing class definitions), and Application (for defining application specific objects).
Conclusions
Geographical information systems involve the creation, storage, retrieval, browsing, and management of spatial data entities associated with maps. A deductive object-oriented data model for GIS which consists of primitive, complex, geographic and logic objects, etc., and their Operations has been proposed. A prototype of the model has been developed using Smalltalk/v, and object-oriented programming language which includes Prolog as one of its classes.
The proposed data model and prototype meet the requirements of GIS mentioned in section 2 in the following ways:
Requirement 1 is met by the employment of object-oriented concept. Various data types and databases can be unified under this concept.
Requirements 2 and 3 are satisfied by the modification and extension of SQL, the de facto standard query language for relational databases.
Requirement 4 is satisfied by the provision of class Application by which application specific features can be implemented.
The last requirement, requirement 5, is, in fact, a goal which has no yet been materialized by the current technology. However, the deductive component of the proposed model provides the proposed model provides the foundation for the development of the learning capability.
References
- CALKINS, H.W. ( 1983), A Pragmatic Approach to GIS Design, International Geographic Union Commission on Geographical Data Sensing and Processing, New York.
- PEUQUET, D.J., (1984), A Conceptual Framework and Comparison of Spatial Data Models, Cartographica, 21, pp. 66.
- SMITH, T.R., MENON, S., STAR J.L., ESTES, J.E., ( 1987), Requirements and Principles for the Implementation and Construction of Large-Scale Geographic Information Systems, International Journal of Geographical Information Systems, Vol. 1, No. 1, pp. 13-31.
- TRINIDAD, G.S., ( 1990 ) ,. A Deductive Database Approach to Geographic Information Systems, AIT Dissertation No. Cs-90-1, Asian Institute of Technology, Bangkok, Thailand.
- Van ROESSEL, J.W., ( 1987), Design of a Spatial Data Structure Using the Relational Normal Form , International Journal of geographical Information Systems, Vol. 1, pp. 33.
