Some database requirements for pictorial applications
In this paper we discuss some functional and performance requirements on a database system to support development of interactive applications dealing with pictorial data. An effort has been made to specify requirements that are independent of a specific implementation philosophy.
Experience using a database system for interactive applications has led us to determine some features that a database system should have. The most important requirement is that the user be able to access data by name, so that programs are independent of the data that they access. This implies that the data is self-describing. The database then provides not only data values, but also a syntatic and semantic description of the data.
An important use of the database is to interpret the data in the file as a picture. This use of the database requires support for ordered files, parameterized files, and support of expressions as data values.
Some requirements for database support of interaction in graphics applications are also discussed. The task of managing tables for interaction is greatly simplified if the database system provides support for self-describing data. The response time constraint imposed on the database system for supporting interactive applications is also discussed. This includes response time considerations for drawing complex pictures as well as the high-speed response for the interaction with the user.
A sample database interface which meets the functional requirements is included. Further research work is needed to translate the performance requirements which are stated in terms of response time for screen activity into database performance requirements for the basic database functions. response to a simple query should take less than 10 milliseconds.
The data stored in the data base that is used for interaction has a much more demanding requirement in terms of response time. When a user selects an item on the screen, the appropriate pick table must be searched and the selected item identified and its tag returned to the application program. Here the requirement is that this operation must take less than 100 milliseconds so that the redisplay of the screen for the new information can take place within the required two second response time.
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