CG&GIS Lab, Faculty of Electronic Engineering,
University of Nis A.Medvedeva 14, 18000 Nis, Serbia
In this paper we present research in Geographic Information Systems (GIS) interoperability. Also, this paper describes interoperability framework called GeoNis. GeoNis uses new technologies, to perform integration task between GIS applications and legacy data sources over the Internet. Our approach provides integration of distributed GIS data sources and legacy information systems in local community environment. The proposed framework uses the technology based on mediators and ontologies, to allow communications between GIS applications over the Internet/Intranet.
Popularity of GIS in government and municipality institutions induces an increasing amount of available information . In local community environment (city services, local offices, local telecom, public utilities, water and power supply services, etc) different information systems deal with huge amount of available information, where the most of data in databases is geo-referenced. Information that exists in different spatial databases may be useful for many other GIS applications. The problem of bringing together heterogeneous and distributed information systems is known as interoperability problem. Today, research on interoperability solutions promises a way to move away from the monolithic systems that dominate the GIS market .
Research in information systems interoperability is motivated by the ever-increasing heterogeneity of the computer world. Heterogeneity in GIS is not an exception, but the complexity and richness of geographic data and the difficulty of their representation raise specific issues for GIS interoperability. Great number of independent geo-data producers, accessible by means of World Wide Web, has only increase problems of heterogeneity.
Interoperability of information systems relies on bases of agreement that describe what is shared among information sources. To enable interoperability, remote systems must be able not only to locate and access data sources, but also to interpret and process retrieved data. In order to achieve this, remote systems had to deal not only with syntactically heterogeneous data objects (objects that are organized following different conceptual schemas) but as well with semantically heterogeneous objects (objects that that have different meaning) [3,4,5].
The paper is structured as follows. In the first part, we describe related work in interoperability, mediation and ontologies in GIS. In the second part of paper, we describe architecture and role of GeoNis interoperability framework. The goals of our research activities, described in this paper, are defining architecture for semantic integration of distributed and heterogeneous GIS data sources and adding the integration technology to the existing framework. Making local geographic datasets available publicly and establishing a common interoperability framework over shared data interchange protocols are important parts of this research.
GIS and Interoperability
GIS applications often have to process geo-data obtained from various geoinformation communities. In that kind of environment problem of semantic heterogeneity often arise. In such cases there is a problem with correct interpretation of datasets obtained from different geo-information communities. Very often different datasets can use different terms for same kind of information. On the other hand different datasets can use same term for completely different piece of information. These problems can lead to serious conflicts during discovering and interpretation of geographic data.
For example let’s consider geographic information system in local community environment [5,6]. In such environment, information provided by GIS application can have key influence on decision make by local community authorities. In many cases this decision are crucial for everyday functioning of the community and for short-term and long-term planning of local community development. Geographic information, used during decision-making process, is originating from different organizations (local Telecom, water and soil service, transport service, power supply service, police and other local government services) in local community (Figure 1).
Very often, as shown in Figure 1, different organizations in local community are interested for same spatial object. But every organization has different view and different understanding of that object, and according to that produce different datasets that describes that object. Some attributes in this datasets are common for all organization in local community, some are common for few of them and every organization can have some specific attributes for dataset. At the same time different organizations can use different terms for same dataset attributes (synonyms) or same term for different dataset attributes (homonyms).
Fig. 1. Local GI community environment
This is a problem of semantic heterogeneity and can lead to interpretation conflicts during interchanging of geo-data. These conflicts can be resolved only by human intervention. Such situation can be acceptable only in case of small amount of data. But in cases of large amount of data (thousands of records) this process can be very tedious and ineffective. This process can be automated only if problems of semantic heterogeneity and interpretation conflicts are solved.
Being seen to “be interoperable” is becoming increasingly important to a wide range of organizations, including central and local government. Interoperability is the ability of two or more systems or components to exchange information and to use the information that has been exchanged [7,8]. Interoperability of information systems relies on bases of agreement that describe what is shared among information sources. Interoperability means openness in the software industry, because open publication of internal data structures allows GIS users to build applications that integrate software components from different developers. Interoperability also means the ability to exchange data freely between systems, because each system would have knowledge of other systems’ formats .
The need to share geographic information is well documented [1,9,10]. Recent reviews of GIS interoperability and integration efforts can be found in [7,8]. Making local geographic datasets available publicly and establishing a common interoperability framework over shared data interchange protocols are important parts of this research.
Although distributed geo-libraries offer numerous advantages over stand-alone geographic databases, there are institutional and technical problems of geo-data sharing and interoperability. These problems have become, over the last several years, the focus of international research and infrastructure efforts and have been discussed at several international conferences and workshops focused on GIS interoperability .
One solution for data exchange between different GIS data sources would be a single architecture and set of standards for geospatial data. A broader discussion of geographic information exchange formats can be found in . One of important strategies for interoperability is conversion of different data formats in common data structure. This kind of data structure is usually based on one of existing GIS standards. However, it’s all but impossible to conceive that the global GIS community would adopt a single geospatial architecture or data standard worldwide. This means that standardization efforts alone won’t produce interoperability.
In the past few years the OpenGIS Consortium  (OGC) has emerged as a major force in the trend to openness, as a consortium of GIS vendors, agencies, and academic institutions. The OGC introduced approaches for effective management of interoperability technology in cooperation with industry and universities. The OGC has identified the need for open geo-data sharing and the exchange of open GIS services.
Despite standardization initiatives, the use of standards as the only worthwhile effort to achieve interoperability is not widely accepted . Since heterogeneity arises naturally from a free market of ideas and products there is no way for standards to banish heterogeneity by decree. As a consequence of two main system characteristic, distributed data sources and their heterogeneity, the realization of interoperability systems is weighty process.
Today, a number of proven and well established methods exist that allow heterogeneous databases to communicate on a technical level, including federated databases and schema integration, object-oriented approach and mediators and ontologies.
GeoNis Generalized Framework
GeoNis is a project that has to provide infrastructure, platform and software tools for data interchange in the local community environment. This project was developed with cooperation from Municipality of Nis and is partially founded by Ministry of Science, Technology and Development, Republic of Serbia.
The goals of research activities in GeoNis project are:
- Defining interoperability architecture for integration of distributed and heterogeneous GIS data sources in local community environment
- Defining a methodology and software support for resolving semantic conflicts in data from different information sources.
The goal of the GeoNis framework is to make the use of different data sources in their GIS applications simple for users. In order to achieve interoperability following six presumptions have to be fulfilled :
- Simple – users should not have to understand all details about the data or their source system to import and use them.
- Transparent – complexities associated with data transfer should be hidden from users.
- Open – interoperability should apply to all systems, and data exchange should be independent of the technology used.
- Equal – systems are equal and autonomous.
- Independence – systems have exclusive right to control its information and information processing without centralized control.
- Effective – data transfer should be reliable, and the resultant data should be useful for the intended purposes.
- Universal – all geospatial databases should be accessible.
- Belonging – each system belongs to one GI community, and has its own institution, policy and culture and value viewpoint.
In local community data sources are services and offices that own geo-data in some format. Specified communities own GIS application, often created with different GIS tools and with different underlying database management systems. GeoNis project for interoperability in local community environment implies several different prerequisites:
- Participants have knowledge of each other’s and data they possess.
- Cooperation between participants.
- Institutional willingness for realization of interoperability. All participants have to agree upon basic principles for realization of interoperability and to provide all needed data and resources.
- Infrastructure for realization of interoperability: network infrastructure (hardware and software), people, organizations and activities, rules and regulations for information exchange.
- Definition of communication protocols between participants
- Development of software tools for realization of interoperability
- Local information sources must be adapted in order to work properly in new environment.
GeoNis is generalized framework for interoperability of GIS applications that have to provide infrastructure for data interchange in the local community environment . Data sources are local services and offices that own geo-data in some format.
Our framework for interoperability has to provide :
- Integration of information from different sources with ability to add new information sources.
- Adaptation of existing data sources and queries without possibility for changing existing data.
- Independence of user applications from information sources
- Solving problems of semantic inconsistence between user requests and available data
Fig. 2. GeoNis framework for semantic interoperability
The basic architecture of GeoNis framework is shown on Figure 2 [6,14] Generic architecture of GeoNis recognizes several different components that have important role in geoinformation discovering and retrieving process:
- GIC – in each node of GeoNis framework there exist GIS application and corresponding (spatial and non-spatial) data sources. Data in these local data sources are accessible according to user privileges.
- Wrapper/translator – component that translates information flow between information source and GeoNis system.
- Semantic mediators – requests for specific data set are forward through.
- Shared GIS server (Catalog Server) – maintains metadata and all shared/common geographic data as addition to domain oriented GIS applications.
- Quality improvement of data due to the availability of complete datasets.
- Improvement of existing analysis and application of the new analysis.
- Cost reduction resulting from the multiple use of existing information sources.
- Avoidance of redundant data and conflicts that can arise from redundancy.
According to GeoNis architecture every GIC environment can have several translators. There can be one translator for every information source in GIC environment. Ginis OLE DB data provider is an example of translator implementation . This approach (unified methods for data access) allows simply chaining of translators. Also we can easily add new information sources without influence on other GIC environments. In order to do this we have to provide semantic mapping only for the GIC environment with new information source. In this way we have simplified the problem of semantic heterogeneity.
The total number of geo-data providers in local community environment is indeterminable and unlimited. This implies the need for a flexible approach that can deal with the existing and the future geo-data providers in interoperable systems. A standard model for spatial data is the first step to approach the solution for schematic and syntactic heterogeneity. The Open GIS Consortium (OGC) specification aims to solve the problem of heterogeneity at the spatial data modeling level. Because of that, GeoNis uses OpenGIS standard as common data model to represent geo-data at mediator level. Data models of local information sources are translated in common model using wrappers.
Semantic heterogeneity of the data sources in GeoNis is resolved using a hybrid ontology approach and methodology (and software support) for semantic mismatches resolving between terminologies. GeoNis solution to the problem of semantic heterogeneity is to formally specify the meaning of the terminology of each GIC using local ontology and to define a translation between each GIC terminologies (local ontologies) and an intermediate terminology (in top-level ontology) . This methodology uses the ontology mappings between each community terminologies and a top-level ontology or the common data model, represented by IF-THEN rules.
GeoNis formal ontology consists of definitions of terms, and it includes concepts with associated attributes, relationships and constraints defined between the concepts and entities that are instances of concepts. In our system architecture it is assumed that the ontology is shared, and there exists commitment by the clients about data, which will be shared. Intent of our formal ontology is for sharing, merging, and querying data, but not for reading and efficient processing.
Interoperability in general, and especially semantic interoperability, will lead to dramatic organizational changes in GI community. Integration of diverse information sources has many advantages:
The GeoNis is a generalized framework, in which both schematic and syntactic heterogeneity is resolved by mediation and common data model. This framework is aimed to resolve interoperability problem in local, municipality environment. Our solution uses a mediator-based architecture for interoperability in local community environment, OpenGIS Simple Feature as the common model, and local ontologies for resolving semantic heterogeneity of data sources. The principles behind the ontology/mediation framework described in this paper are extensibility, relative autonomy of infrastructure nodes, and universal access to heterogeneous data sources from a variety of portals.
GeoNis uses widely accepted OpenGIS standard for geo-data modeling and representation on the mediator level. Changes in the OpenGIS standard have impact only on translators, not on information sources. GeoNis also enables adding legacy data sources in interoperability process. The only condition is the translator realization (implementation).
Significance of our work is based on usefulness of GeoNis tools and components for realization of interoperable geo-spatial and other (such as B2, see ) information nodes in local community organizations.
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