Chaining Façades: Higher Efficiency in evolution-enabled Spatial Data Infrastructures (SDI)

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1 Chaining Façades: Higher Efficiency in evolution-enabled Spatial Data Infrastructures (SDI) Roland M. Wagner Fraunhofer ISST, Berlin/Dortmund, Germany ABSTRACT After the first publication of the known Web Mapping Service by OGC in 2000, more and more web service specifications appear. Also many different versions of these services appear. From a commercial point of view, the functionalities authentication & authorization and pricing & ordering are required for many business models in a spatial data infrastructure. Of course, these functionalities should support the growing number of services. But this requires an understanding of the specific content structure of the service protocol and a special chaining. A solution is the façade approach, which concentrates the protocol-specific parts. The introduction, administration and updating can be automated by using a Registry and a Façade Service, which is described in this paper. KEYWORDS: geodata-infrastructure, chaining of services, pricing, ordering, e-commerce, authentication, authorization INTRODUCTION After the introduction of the OpenGIS (OGC) Web Mapping Service Implementation Specification in 2000, the set of usable and interoperable part-solutions for a Spatial Data Infrastructure (SDI) has grown significantly. Examples of the Global Spatial Data Infrastructure Initiative (GSDI) show the usability for free spatial data and information in many parts of the world. The ideas of a visionary group who met in Bonn at the beginning of the nineties are getting more and more reality today. Because of high costs for collecting and maintaining spatial information, the question of refinancing is relevant and is handled differently at the providing public and private institutions in different countries. Beyond private provider, many public institutions in Europe have a (part-) refinancing policy. In some cases, laws restrict the distribution of spatial information and attributes to special user groups. In other cases, the distribution of private spatial data should only be limited to user within the same organization, but at different locations. Therefore a Spatial Data Infrastructure needs to meet these enhanced requirements of Pricing & Ordering and Authentication & Authorization for general acceptance. But different principle functions will result in different protocols. The Web Pricing & Ordering Service (WPOS) and the Web Authentication & Authorization Service (WAAS) are used implementation specifications, which were developed in the GDI NRW Testbeds. The WPOS specification was already contributed to OGC and deployed in Brandenburg and in NRW (Wagner 2002). 1

2 Embedding new Functionalities into the existing OGC Framework Beyond the different functionalities, a new web service chaining mechanism, which is still cascade-able and not implementation dependent, was required and was developed to meet the problem of crossing and depending information streams. Also, a solution should be implementation independent to support existing and installed implementations all over the world. These implementations need to be considered as black boxes with only the known interface. The process is described in detail in a dissertation (Wagner, 2003). A typical use case for dependencies is the price, which is based on a selected area. But the area, or bounding box, is defined in a released (and therefore strict-defined) OpenGIS protocol specification. Additionally there might be different versions of the same OpenGIS protocol specification. Nevertheless the bounding box data needs to be extracted from the concrete protocol into a general translation model, which could be matched to the WPOS pricing model. Another example is authorization. If a user sends a WFS-specification request to a secured database, the request might contain a read, which should be accepted, but the same request may also contain a write or delete, which should not be granted. A Web Authentication & Authorization Service (WAAS) needs to analyse the specific request to look for the concrete actions within the concrete protocol. To meet the mentioned implementation independency, any solutions can only be chained within the expert client and service communication stream. This means also that each manipulation tier needs to simulate a known interface. Figure 1 shows an example with a Web Mapping (WM) (De La Beaujardière, 2001), a pricing & ordering (WPO) and an authentication & authorization (WAA) tier. The WPO-Client needs to simulate a. A WAA-Client needs to simulate a WPOS. The protocol-specific translation and manipulation component is called façade, because it is only attached to the general structure, e.g. the geo-ebusiness client and service component structure. The structure is needed for a more general functionality. Therefore only a façade is required for each protocol and version. Figure 1: Overview of Protocol Manipulation Tiers 2

3 The expression façade is also an image for the relationships between protocol-specific parts and general functionality. A façade has only limited functionality but is good for simulation. The following figure 2 shows the same chaining only with different views. The security layer was neglected. -Client WPOS-Client WPOS-Server -Server 2a Request 2b Pricing Pricing Ordering 2b 2c Request Response 2f Delivery 2e Response 2d Client Service Figure 2: Protocol Manipulation Tiers without WAA 3

4 The figure 3 shows the ability to cascade the solution. Cascading is a core mechanism to integration and to distribute organizational and/or physically distributed spatial information. -Client Company A WPOS-Client Company B WPOS-Service -Service -Client Transparency WPOS-Client Company C Company D WPOS-Service -Service WPOS-Service -Service Figure 3: Cascaded Protocol Manipulation Tiers The WPOS was the first service using this new service chaining mechanism in the SDI sector. But it can also be used for the complete automated processing of the chain searching & finding, authentication & authorization, pricing & ordering and data access. Because of many different interoperable and known OpenGIS implementation specifications like Web Mapping Service (), Web Feature Service (WFS) or Web Coverage Service (WCS) with HTTP GET or POST profiles, in different versions and also growing proprietary service applications protocols,, on the one hand and on the other hand different industrial or geo-sectorspecific standards like HTTP/SSL, SAML and ISO 19115/OGC WRS,, the matching mechanism in a distributed environment needs to be solved in a sophisticated way (ISO 2001). It should also be possible to use different parallel (part-) solution chaining. A useful example for the parallel chaining is the offer of different (industrial) security protocols. If hackers crack a security mechanism, the SDI could quickly shut down the hacked specific part solution and other parallel solution could (still) be used automatically. 4

5 Figure 4 shows an extended version of figure 2. Because of an open number of protocols and versions and expected permanent update and install requirements, the download of suitable façades should be automated completely. Figure 4 shows an example with a WPOS and a. An encoded request arrives from a client. The WPOS does not have a suitable façade, therefore a search request will be send to Web Registry Service (WRS). The response contains the URL of a suitable Façades Service, which will be requested. WPOS-Server -Server Web Registry Service Façade Service 2b Pricing GetWPOSFaçadeService (OGC,, v 1.1.0) WPOSFaçadeService URL Publish translaterequest 2c Request Response 2d Service Figure 4: Cascaded Protocol Manipulation Tiers Some experiments showed that the façades for a HTTP GET and for a HTTP POST WFS could be completely expressed in a single XSL file. But to be more general, a Façades Service should be introduced. A Façades Service may also provide additional operation, e.g. to detect protocols and versions. The introduction of Façades and Façades Service can lower maintenance costs by automated and remote upgrade/update/downgrade of distributed service implementations belong organizational borders. It enables quick and rational introduction of proprietary application protocols together with known protocols. This approach lowers investment risk by using mainstream solutions for parts of the chain and it lowers risk for failure of complete SDI infrastructures due to illegal cracks. 5

6 Finally it provides a key technology to set up a full commercial-enabled SDI. Therefore the introduction of façades provides higher efficiency in an SDI. Figure 5 gives an overview and classifies resulting Geo-eBusiness variations, which uses façades inside. Figure 5: Geo-eBusiness Variations BIBLIOGRAPHY ISO ISO/TC 211: ISO Technical Committee 211: final, Geographic information Metadata, January De La Beaujardière (2001). Web Map Server Interface Implementation Specification. Open GIS Consortium, 2001, ( Wagner, R.-M. (2003). A Model For The Digital Representation And Transaction Of Complex Pricing And Ordering For High-Value Spatial Products And Services., Dissertation, TU Berlin, Berlin, Wagner R.-M. (2002). Web Pricing & Ordering Service, accepted OGC Discussion Paper, 02-39r1, OGC,