Wencai Du, Yair Gabay
*The Center for Geographic Information Sciences
Technion-Israel Institute of Technology
Haifa, 32000, Israel
Email : [email protected], [email protected]
Tourism is an information-intensive and information-sensitive industry in which electronic commerce, WebGIS, and Internet technologies are expected to play a significant role. It is evident that both the way the information is presented and the approach to tourist searching for information has a great impact on the tourist’s decision and satisfaction.
vWith the tremendous growth of the Web, today, all types of Tourism Information (TI) providers already have homepages on the Web for storing the comprehensive description of the tourist destination and for presenting tourism products. Almost all homepages support static HTML-page. However, the problem is that HTML was designed specifically to describe the presentation, not the content. There is nothing in the HTML text to make it easy for other programs to understand the structure and content of such data. Existing TISs built on HTML are a lack of dynamic, scalable, extensible and interactive functionalities. They are also unable to integrate geographic data and tourism information. They fail in accessing and exchanging the data available in heterogeneous TISs. These limitations have pushed for the need for more sophisticated information system and web standards, such as WebGIS, XML and SVG technologies.
The challenges are how to present information related to tourism on the Web and to access to multiple, distributed, heterogeneous and autonomous information sources. One of the solutions is through establishing a WebGIS-based TIS and creating flexible data interchange facilities in the system, thus allowing dynamic and interactive presentation of tourism information and interchange of data with other TISs. Information technologies, for example, web-based GIS and XML-based technology, can be expected to meet these challenges.
vIn this paper, we investigate the design of WebGIS-based TIS using XML and SVG technologies. We present an architecture for such a tourism information system, and describe such prototype Tel Aviv WebGIS tourism Information System (TATIS). The prototype does not currently implement all the features and components that we present in this paper, but the most important elements are already designed.
2. Design of WebGIS-Based Tourism Information System
2.1 Design objectives
The tourists play the main role in tourism. Thus, the purpose in designing this WebGIS-based TIS is to improve the contact with the tourist through better, more attractive, multimedia and up-to-date information, in particular digitized information in the form of text, image, videos, sound, etc. as well as instantaneous information such as availability of rooms and seats. Thus, to design TATIS has to focus on the content aspects by providing detailed, accurate and actual tourism information and by offering vividly presenting the information on the system as well as providing appropriate search mechanisms. Using the system, users may obtain a comprehensive, accurate and up-to-date tourism information on Tel Aviv and all destination facilities, places worth seeing, and certain tourism products can get attracting view of the destination, and can buy products either offline or online. By providing better information the tourists might be more satisfied and willing to spend their holidays in Tel Aviv.
2.2 Prototype Development
This system is based on a three-tier architecture, from top to down, consisting of graphical presentation layer, a structure management layer and database management layer (Figure 1). TATIS web site construction involves three tasks: managing the tourism information presented at the site, managing the structure of the web site, and creating the graphical presentation of the SVG pages in SVG or HTML formats.
Figure 1 Architecture of integration of WebGIS and tourism information system
The function of data management layer is to integrate tourism data from multiple, heterogeneous sources into a single semistructured data repository called the data graph. The data graph is stored in a text file in a syntax layer. The data integration part of TATIS is standard: there is a wrapper for each source and specific mediator. Each wrapper translates the tourism data from the source’s logical model to TATIS’s logical model. The structure makes it easy to add a new source only by making the one-time effort of writing a wrapper for that source. The mediator integrates logically the data from several sources and is defined by a query.
The function of structure management layer is to manage the structure. Here we construct a site graph that encodes the TATIS web site’s structure using XML and SVG technologies; nodes correspond to SVG pages, or components thereof, and edges to hyperlinks or to component inclusion. The site graph is constructed declaratively by XML query language from the data graph.
The function of graphical presentation layer is to describe the graphical layout in SVG templates for end users via the public Internet, which are input together with the site graph into the SVG generator to create SVG files. This layer allows searching for topic-oriented information and route planning information by hierarchical navigation and complex structured searches. The layer represents dynamic and interactive vector graphics using SVG. In contrast to exiting most conventional TISs on the world, this new design poses fundamentally new challenges: The geographic search for tourist objects and dynamically generated tourist maps.
TATIS uses SVG DOM standards to interface with Web tools and editor in order to specify mechanisms for querying, processing, and retrieving of data. SVG DOM is an API for SVG documents. The advantages of this approach is that SVG DOM is a platform- and language-neutral interface that will allow programs and scripts to dynamically access and update the content, structure and style of documents. The document can be further processed and the results of that processing can be incorporated back into the presented page.
3. XML-based Data Integration
The integration of geospatial data from heterogeneous data sources is a challenging problem when trying to utilize existing TIS on the web, because of heterogeneity of sources and lack of source metadata. Another new challenge occurs in the integration of GIS and TIS. The reason is that GISs were originally developed independently by software vendors, who tailored their applications for their specific user needs, using locally created terminologies and approaches (Goodchild 1999).
In the TATIS, the information integration of geospatial data which are stored in GIS database and tourism data in TIS are achieved by using a two-part middleware between the information sources and the tourists’ application (Figure 2). The first part is called a mediator. Its function is to accept tourist request, breaks up the request into small fragments according to the capabilities of the sources and delegates the request-fragments to the appropriate sources. When the sources process the requests and return the results, the mediator integrates the results and sends the combined information back to the user. In the process, the spatial mediator browses the schema information exported by GIS wrapper as an XML DTD, and dynamically evaluates the minimal combination of sources that satisfy the query attributes and predicates. The aspatial mediator integrates and transforms data from several sources using a declarative specification. For example, it is used to convert aspatal data between different models by translating data from a relational database into XML format and integrating data from different sources into a common view. The key technology in the mediator consists in query rewriting.
Figure 2 The spatial mediator and XML-wrapped sources of geospatial data and GIS and TIS services
The second part of the middleware is called a wrapper. The task of the wrapper is to translate a request from the mediator’s language to that of the information source and transform the results provided by the information source back to the mediator’s language. Acting as a proxy of an information source, the wrapper communicates with an information source in SVG DOM, and communicates with the mediator in XML and SVG. In this way, “wrapping” each information source into the translation software makes the protocol diversity of particular sources manageable.
4. Strategies for transferring data between XML documents and relational databases and middleware
As design examples of our work, we discuss the strategies for transferring data between XML documents and relational databases according to two mapping rules of a table-based mapping and an object-based mapping. The table-based mapping views an XML document as a serialized table or set of tables. The following code is the example of structure of the document.
From the above text we can see the table-based mapping has the advantage of simplicity. Simplicity makes it useful as a model for writing data transfer tools, especial using XML to transfer data from the relational databases. Furthermore, the code to transfer data between an XML document and a relational database is independent of whether SAX or DOM is used. The reason is that the table-based mapping allows the document to be processed in single pass in document order. The table-based mapping is commonly used by middleware to transfer data between XML documents and relational databases.
In TATIS we store some data in object-relational model. For this case, we adopt an object-relational mapping to transferring the data. Contract to the table-based mapping, the object-relational mapping views an XML document a tree of data-specific object and then uses an object mapping to map these objects to the database. In this model, elements types with attributes, element content, or mixed content are generally modeled as classes. Element types are modeled as scalar properties. The model is then mapped to relational databases using traditional object-relational mapping technology or SQL objective view. That is, classes are mapped to table, scalar properties are mapped to columns, and object-valued properties are mapped to primary key/foreign key pairs. For example, the following figure shows the structure of the XML document (Figure 3).
Figure 3 Structure of XML document using object-relational model
5. XML-Based Virtual Map Interfaces
In TATIS, query results are returned as map and tabular data from the mediator to the user interface on a Web client based on SVG rendering capabilities of Internet Explorer 5. The results of the integration of GIS data and tourism data will be touristic maps including the information where touristic objects are, how they can be reached, and which objects are located nearby. SVG allows to interact, analyze, and use screen-related functions, such as zooming and panning. It will lead to change in maps from static raster graphics to interactive graphical representations that allow the presentation of the most extensive information possible thus satisfying the demands of the users.
6. Conclusion and Future Work
As discussed in the previous section, TATIS framework based WebGIS and XML-based technologies, for integrating distributed and heterogeneous data elements of TISs have been proposed. In contrast to exiting most conventional TISs in the world, this new design poses fundamentally new challenges: the geographic searching for tourist objects and dynamically generating scalable and interoperable tourist maps. The architecture of this system is logical integration for geographic information stored in a GIS system and tourism information stored in database management system. This approach to present integrated GIS and tourism information is based on the following concepts: a powerful geographic search which is the base to create dynamically generated vector maps in SVG which are enriched with additional tourism layers, to offer the users fast, flexible and meaningful access to the data to fulfill their requirements. The value of this study and its implications lie in providing us with an initial set of relevant technologies, requirements and issues to consider the in development of WebGIS-based TIS using XML and SVG.
We also create some API using XML and SVG programming. We will develop a prototype for implementing and testing, and this prototype will be implemented fro the tourism information system in Tel Aviv City of Israel.
- Goodchild, Michael. Preface. Interoperating Geographic Information Systems. Edited by Goodchild, M. & Egenhofer, M. & Fegeas, R. & Kottman, C. Kluwer Academic Publishers 1999.
- W3C 2001 XML Query Requirements, https://www.w3.org/TR/2001/WD-xmlquery-req-20010215.