Distributed Hypermap Model for Internet GIS

The rapid development of Internet technology makes it possible to integrate GIS with Internet, forming Internet GIS.Internet GIS is based on the distributed Client/Server architecture and TCP/IP IIOP (Internet Inter Object Protocol).When constructing and designing Internet GIS, we meet with many problems, such as how to express the information units of Internet GIS. For Internet GIS, the expression of spatial information unit is a key issue.The perfect description should satisfy with data access and operation of spatial information.Several concepts were developed to express the information on Internet, i.e, hypertext, hyperdocument, multimedia, hypermedia, hypergraph, and hypermap. Hypertext refers to a set of nodes connected by links that offer the user a non-sequential tour around the data; Hyperdocuments introduces multimedia components into the hypermedia concept.Hyperdocument is really special hypertext, including image and sound, etc; Multimedia is a mixture of media, including text, graphics, picture, video, sound, panoramic picture, interactive movies, annotated movies, 3D virtual reality, taste, odors, tactile sensation, etc. The concept of hypermap was described by Laurini (Laurini, 1990), as a multimedia hyperdocument with geographical access.Geographical access implies access by geographical coordinates.The idea behind the concept was the desire and ability to retrieve all documents related to a certain area.The area could be indicated by clicking an object or region in a map or defining a search window.The hypermap thus allows the user to make a geographic search, in addition to a thematic search.Using a hypermap, for example to retrieve spatial information based on associative and logical combinations, is expected to be an efficient and easy method to understand the environment (Laurini, 1992). From the object-oriented principle point of view, in fact, hypermap (H) of the distributed hypermap model (DHM) is a set of spatial object (O^S). Every spatial object O^S consists of four elements.They are object identification (ID), hypermedia (H^M), hypergraph (H^G) and hyperlink (H^L), expressed as: O^S=ID^S, H^M, H^G, H^L Where, ID^S is the object identification; H^M is the un-geometrical attribute, i.e.multimedia attribute (A^M); H^G is the geometrical attribute, i.e.spatial attribute (A^S). H^M and H^G consist of the internal states of O^S. H^L is the method set of O^S, in which the un-sequent operation methods and linking relations of internal object and internal or external hypermap are involved. In this new model, hypermap consists of hypermedia, hypergraph and hyperlink.Hypergraph constructs all graphic attributes and hypermedia defines all multimedia information of hypermap.The links between hypergraph and hypermedia are realized through hyperlink.Hypermap is the union of hypermedia, hypergraph, and hyperlink. H=H^M∪H^G∪H^L This new hypermap concept is different from the old model (Kraak's definition) in two points.The first is about the type of information expression.The old hypermap model is the combination of hypermedia and geographical coordinates.Its emphasis is to complete the browsing on hypertext and hypermedia.The new model, based on oriented object concept, considers both hypermedia and hypergraph as the attributes of geographical information (e.g.multimedia attribute, spatial attribute, forming the internal state of geographical information attribute).Hyperlink is considered as the set of operations, non-sequential link relations between object internals and objects, and hypermap internals and hypermaps.The second is that the purposes of both concepts are also different.In Kraak's concept, hypermap is the hypermedia that navigates through geographical coordinates.In the new model, 4D spatial description, browsing, multiscale information management, metadata, content, clearhousing are defined.Besides the functions of navigation and browsing, the new model is expected to fulfill all functions of GIS in the distributed ways, such distributed components and distributed computation, in order to construct Internet GIS and manage information of Internet GIS. The relationship of hypermap in the distributed hypermap model refers to the inside relationship of certain hypermap and relationship between any two hypermaps.The inside relationship of certain hypermap involves the inside relationship of hypermedia and hypergraph, and the relationship between hypermedia and hypergraph each other. Finally, the authors give the case study of Internet GIS, using the distributed hypermap model (DHM).In the prototype of Internet GIS,we use distributed hypermap model to organize and manage GIS information on the Server.Distributed hypermap and distributed components are the core parts of the prototype.Meanwhile,we use hypermap to finish the most of GIS functions.