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Track: Application Development
Steve Allenstein
University of Wisconsin
2208 Center Avenue
Madison, WI 53704
Telephone: 608-263-5534
Fax: 608-262-2500
Model-Based ArcView Application Development
Defining Issue: Once an ArcView application has been developed for a particular client and problem context, it can be difficult to reuse in other similar circumstances. When adapting such applications, major code revisions are often needed due to differences in underlying data models and in the logical views of the spatial database desired by different clients. Also, the difficulty of revising Avenue scripts increases with the size, complexity, and functional scope of the application. Such problems are not limited to ArcView/Avenue development. GIS Solution: This paper examines a software approach. Using Avenue, a generic model of an application and its database is encoded into an ArcView/Project. The model can then be customized to different situations, an operation that is much more efficient than revising code. The technique accommodates the transformation of different data models into that of the generic model. It may also be generalized into an object-oriented framework that employs a truly
extensible programming language. In an interagency context, this and similar techniques might be used in conjunction with "Data Model Content Standards" to afford common data views. Methodology: The methods discussed in this paper were developed as part of an application involving a consortium of eight county governments, a private consultant, and University researchers. The purpose of the application is to develop a generic ArcView interface to local land records that might be used by a local LIO or in a tax assessors office. Specifically, the application is to support nominal browsing and query operations on tax parcel tables, parcel coverages, and related land information. The initial phase of the project is focusing upon issues related to implementation within an agency context. Later phases will be concerned with public access to information contained in these databases. A generic model is developed by simulating the creation of higher-level objects relative to those available in ArcView.
Examples of such objects include "Screens" which organize the visibility and placement of ArcView documents on-screen, "Layer"' which aggregate component ArcView themes, and so forth. Associated functionality includes "Doc Menus" which augment the standard ArcView interface with controls that contain instructional text, a "Tile Manager" which dynamically coordinates the display of tiled themes, and a "Query Manager" which accommodates the use of custom search techniques, custom indexes, and alternative means of organizing thematic attributes. The model is specified through entries made by the developer in ArcView table documents. Customization is accomplished in a similar manner, by adjusting the table entries, or more dramatically by deleting or adding new table records. For instance, an ArcView theme may be respecified in a different context by entering the local path to the data source, under the appropriate record and field in a table. Software: The application and the techniques discussed in this
paper were developed solely using ArcView and Avenue.
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