GIS Functional Component Library and Function Integration

In recert years,with the emergency of commercial distributed-computing infrastructures such as DCOM and CORBA,and the increasing need for interoperability of independently developed software "chunks",components and component-based software engineering (CBSE) have gained substantial interest in the software community. CBSE brings architectural thinking to the center of the software development process.It clearly separates infrastructure from system logic and helps to cope with system complexity.It helps organize large-scale development and,most importantly,makes system building less expensive.Compared with other application development,GIS has its own characteristics.As we know,only huge and complete GIS software can be released as GIS platform,at the same time,most of GIS application development are based on certain GIS platform,while only a few functions of GIS platform are used in the application development,which leads to great waste in resources and funds.Until now,many application development are united as "workshop",on the one hand,the programmers developed the function/module from the bottom according to one user's request;on the other hand,many programmers developed the same function/module according to the specific requests,thus led to repeated development of the same function.And this "workshop" development mode needs more time and more funds.The use of CBSE will avoid such disadvantages.As component technology has begun to impact the process of software development,it turns the traditional developing mode of "workshop" to the new mode of "component production" and "component integration". Now there are many GIS functional components:Mapobjects (ESRI corp.),MapX (Mapinfo corp.),Geomedia components (INTERGRAPH corp.),etc.With the development of component technology,there will be more and more components.How to manage these components and how to make good use of these components are one topic of this paper.The paper brings forward the concept of GIS functional component library,which is used to manage the components and make it convenience for people to select the proper component.Considering GIS particular characteristic——spatial information,GIS functional component library is discussed from its organizational structure,access,retrieval,evaluation,etc.Distinguished from other libraries,the description contains more information of GIS component,including spatial data form,applying object,domain and aiding software,etc.Spatial data form means projection,coordinate and data format,etc.Applying object distinguishes attribute information from spatial information.Domain emphasizes the component reuse.According to GIS functions,we classified the component into eight categories:input,edit,display,query,analysis,output,management and others,then they can be further divided according to spatial information or aspatial information.Thus,we obtain clustering of the similar function.After that,we take five-element-group description,which includes function,applying object,support media,domain,applying region,and facet weight concept figure to distinguish similar function and select proper function.Based on the GIS functional component library,with consideration to GIS spatial and aspatial characteristic,five-level integration construction was proposed.It includes user schema,integration schema,spatial and aspatial schema,express schema and local functional schema.Finally,an instance was provided as the example of "component production" and "component integration".