Interoperating Geographic Information Systems

The integration of software components is often times seen as an engineering task, much like designing a converter from 220 to 110 volts so that appliances that were designed for 220 volts can be used in another environment. However, limiting the discussion of interoperating GIS to such an approach would miss a significant aspect: the semantics of geospatial information. We cannot talk about how to approach interoperating GIS without knowing what the software integration process should address.

Interoperability has been a basic requirement for the modern information systems environment for over two decades. How have key requirements for interoperability changed over that time? How can we understand the full scope of interoperability issues? What has shaped research on information system interoperability? What key progress has been made? This chapter provides some of the answers to these questions. In particular, it looks at different levels of information system interoperability, while reviewing the changing focus of interoperability research themes, past achievements and new challenges in the emerging global information infrastructure (GII). It divides the research into three generations, and discusses some of achievements of the past. Finally, as we move from managing data to information, and in future knowledge, the need for achieving semantic interoperability is discussed and key components of solutions are introduced.

The development and deployment of successful interoperability strategies requires standardization that covers many application areas, many different views and conceptualizations of the world. Interoperability between computing infrastructures needs—much like every information exchange—a set of common rules and concepts that define a common understanding of the information and operations available in every cooperating system. Standardization processes and interoperability initiatives such as those of the Open GIS Consortium try to provide an agreed-on set of such rules and concepts. Standardization processes are often driven by market forces and vendors trying to position their particular technology and product as a common concept. However, in spatial information systems (and also other areas) the common concepts include not only technical aspects but also fundamental questions on modeling spatial, real-world features, that is, problems which are beyond a specific technical approach and implementation.

The Open GIS Consortium (OGC) is a consensus-based association of public and private sector organizations dedicated to the creation and management of an industry-wide architecture for interoperable geoprocessing. It has a different perspective on interoperability from that of most technology developers and users because its focus is on user-centered business and purchasing models based on interoperable geoprocessing. OGC is driven by business needs and opportunities, and provides a forum for conducting rational industry planning processes

Interoperability between different data sources and software systems is difficult to achieve due to the complexity of geodata. This complexity is caused by various factors, such as the underlying digital formats imposed by a particular software or acquisition method and the complexity of higher level descriptions, conventions, and rules imposed by individuals, organizations, and disciplines using the software (Buehler and McKee 1996).

Geographic information systems (GIS) employ distinct conceptual models of geographic space (Goodchild 1992), often as a reflection of the origins of the software (e.g., computer-assisted design and image processing). Some of these models are radically different, such as the images employed by Idrisi compared to the object coverages used by ARC/INFO. Others are more subtly different, such as a topologically-oriented coverage compared to the spaghetti polygons used by many desktop GIS. The meaning of spatial data is not the same within these models (Morehouse 1990), and translation or interoperation that is based solely on the geometry can lead to logical inconsistencies within the translated data. Whilst a good deal of very useful progress has been made by the likes of ISO TC211 and the Open Geodata Interoperability Specification (and related models), as yet these standards fall somewhat short in addressing the semantics of the underlying geographic models. Efforts thus far have tended to concentrate on geometry, which can be rather ambiguous in defining the meaning of data in a geographic sense.

Interoperability can be understood in a number of ways. In a minimal sense, even the capability to transfer data from one computer system to another without transformation loss can be identified as interoperability. In a broader sense, interoperability can be taken to suggest the ability of different applications to interact dynamically, facilitating the smooth interface of multiple information sources. This chapter examines interoperability in this second sense, specifically the role of semantics in facilitating the exchange of information.

In the area of geographical information systems (GIS), the requirements posed upon a set of heterogeneous but interoperable systems are not easily met. The particular systems most often possess a certain degree of autonomy and are designed to meet specific requirements for their respective application domains. In order to be more than mere data exchange, interoperability needs to be based on a framework which is easy to understand for all participating communities and yet expressive enough to meet those application-specific requirements. One of the most difficult problems when designing such a framework is to find an appropriate depth or thoroughness of the items specified, that is, the question of what should be specified and what should be left to particular implementations. An interoperability specification that leaves many things open to the implementation is usually easy applicable but maybe not very useful if important things have been left out. In contrast, a specification that includes too many details and assumptions might avoid semantic heterogeneities and similar problems, but fail in acceptance by the software industry because it leaves no room for innovation and competitive differences. The decision on how much to specify is basically a question of the level of abstraction and can be compared to various abstraction levels that are used, for example, in layered software architecture (e.g., the ISO/OSI communication model; Stevens 1990). Such architectures are a result of vertical (in terms of abstraction) and horizontal (in terms of purpose) decomposition of complex computing systems, where the borders represent the interfaces defining the decomposition.

Today, a promising approach to large-scale interoperability in geographic information systems (GIS) is a GIS implemented via a distributed object management system (DOMS; e.g., CORBA, Java, OLE/COM) based on a standardized spatial object model (e.g., OGIS; Buehler 1996). Geographic entities are available as location-and platform-independent objects, and are accessible via their interface, that is, their attributes and a set of operations. Using a DOMS, much of the hardware, network, and communication heterogeneity between interoperating GIS objects on different platforms and machines is handled automatically by the DOMS software, and is of no concern to the user. Also, via the notion of strongly-typed object interfaces, type checking is also performed automatically at compile time to ensure that correct argument types are passed between interoperating GIS objects.

Specifications of software interfaces are essential for interoperability. If an interface is not clearly specified, software that exposes or uses the interface necessarily contains assumptions that can make it non-interoperable with other software based on different assumptions. Eliminating, or at least coordinating such assumptions requires a precise and complete specification language. If such a language also allows for prototyping of the specified components, it is a much more powerful tool in the specification process and can even support conformance testing. This chapter describes why and how functional languages serve all these purposes.

Much of the motivation for the drive towards interoperability in the past few years has come from the enormous power of the Internet and its applications, particularly the World Wide Web (WWW). Five years ago the Internet was an interesting way of connecting computers; today, it is the basis of an industry that is registering explosive growth and intruding into many aspects of our lives. It is commonplace to compare the WWW to traditional libraries: instead of books that take years to publish, and are deposited relatively inaccessibly in massive physical structures, the WWW allows everyone with a simple electronic connection to be an instant publisher and a reader of up-to-date information. With the WWW, we appear to be drowning in information.

The extended use of GIS varies from simple map making to environmental modeling. In each, different users have specific data needs, formats, and most important of all they possess unique problems. As a response to this, the majority of GIS vendors supply a normalized GIS-in-a-box package, containing the data structure, formats, and geographic functions that will ultimately impose the vendor flavor in the design and operability of the problem. The user becomes limited in the design of his or her own problem to the functions supported by the vendors. On the other hand, the need to increase market share imposes a constant need to upgrade the spatial functions and data structures available. This creates an exponential growth in software complexity. In the long term the user depends on data and software standards and needs constant upgrades to training.

Solutions to spatial problems often impact a variety of stakeholders. Geographic information systems (GIS) and spatial decision support systems (SDSS) provide useful tools for the analysis of spatial problems and can be used to investigate the impact of alternative solutions on individual stakeholders. These technologies are, however, often expensive and difficult to implement. As such, some suggest that GIS and SDSS provide an unfair advantage to those with the economic means needed to implement the technology.

Interoperability within geographic information systems (GIS) is concerned with both data and operations. We focus here on the data aspect, more specifically on the access to multiple, distributed, heterogeneous, and autonomous information sources and on their integration. For this purpose, we need to take into account the special requirements of applications dealing with geospatial data, such as:the vast amounts of data considered;the existence of complex and highly-structured data;the co-existence of many different geographic formats;the increasing trend towards reuse of geographic data all over the world;the distributed nature of geographic data.

This chapter goes beyond the exchange of spatial information to look at how tools for manipulating that spatial information are commonly understood and transferred across application boundaries. In this respect interfaces for spatial information systems are examined at a conceptual level. We are more concerned with the expression of user requirements and system structure than the component level interfaces between system modules.

This chapter presents a prototype system which allows the geographic information user to locate data efficiently. By adapting ideas from business systems research (particularly from the field of multi-agent systems), a distributed network of information brokers has been designed. These information brokers understand geographic metadata and use it to communicate with the user through a graphical user interface (GUI). This approach removes many of the disadvantages of general Web search engines (which have no understanding of metadata). Furthermore, it allows specialised information brokers to be created, which can be situated in the best part of the Internet for their user community. This overcomes a major problem with current geographic metadata servers, where a server in America becomes unusable from Europe at most times of the European working day.

Geography is by its nature interdisciplinary, and almost any geographic task involves the integration of a wide variety of information about the world. The primary advantage of geographic information systems (GIS) over other methods of analysis has been their ability to overlay various types of geographic information visually; however, the primary drawback of GIS has been the difficulty of collecting the necessary data before one can do anything interesting. Because obtaining data directly from the field usually requires considerable time and financial resources, one would prefer to obtain existing data from another source if possible.

The following dozen chapters expose the full complexity of the geospatial interoperability challenge: there are both problems and meta-problems. The problems stem from the special functional needs of any particular GIS application. Each particular geospatial application, such as those found in each of the twelve chapters of this section, needs a number of unique services that must be specially designed. Examples include custom portrayals, special data access and retrieval capabilities, information parsing and restructuring, persistent and transient storage requirements, communication needs, and many others. Here, the tools so carefully crafted for the general case are often revealed to be too slow, too weak, or too narrow for immediate use in particular real world applications. That is, each project exposes the need for new software implementations for what should be routine applications.

The theme of our work is intelligent support to users in exploration of spatially referenced data. Under spatially referenced data we mean various thematic data (data on demography, economy, education, culture, history, etc.) referring to geographical objects or locations (countries, regions, cities and so on) rather than purely spatial data such as geometry of geographical objects and their relative positions with respect to other objects. Spatially referenced data cannot be effectively analyzed without representing them on maps. However, a number of different presentation techniques exist, and selection of proper techniques in accord with data characteristics is crucial for successful analysis. An improperly designed map can be unhelpful or even mislead the user into wrong conclusions.

Today a typical geographic information system (GIS) is a complex software package which inevitably inherits the software-engineering practices of the past. Application programming within such systems is extremely complicated. Data structures and functions are often completely hidden from the user. As a result, they are hardly extensible to meet the requirements imposed, for instance, by 3D and 4D modeling. The next generation GIS should benefit from modern software engineering technologies, among which one of the most promising is component-based design. Software building organized in libraries with consistent programming interfaces will enable the fast assembly of special-purpose applications for particular domains. An application-specific component can be customized and re-used (with necessary extensions and modifications, if required) for the development of related applications. Following this approach, today’s general-purpose GIS will be replaced by a family of specialized sub-systems which, due to their common design basis, are well suited for inter-communication and mutual data exchange.

In 1994 NASA issued a Cooperative Agreement Notice to support new research on digital library technology that would enable broader public use of its Earth science data over the Internet. As a response to this CAN, the Universal Spatial Data Access Consortium (USDAC) was formed and it proposed to prototype the GeoLens system that would not only give broader public access to NASA’s Earth observation data, but also made these data interoperate with other geospatial data served by the Federal government. Part of the challenge of the GeoLens Project has been to decompose the larger geospatial interoperability problem into constituent issues. This chapter will address these issues and describe solutions implemented in our GeoLens prototype. The purpose of this exercise is to support an end-to-end scenario, beginning with geospatial data discovery and ending with conflation of geospatial data extracts from extremely heterogeneous sources. The larger goal is to investigate the opportunity for new information processing standards and innovative digital library technology to play a key role in the realization of this scenario.

The need to access multiple databases arises frequently in geographic information processing because a single spatial object database may not contain all the information at the desired level of abstraction, completeness, and accuracy. For example, in planning the extension of underground urban utility networks such as gas and telecommunication lines, it is necessary to access databases of existing and planned utility networks. Such databases are usually maintained independently by individual operating companies. It is also common that these independent databases maintain much geographic information redundantly with different levels of abstraction, completeness, and accuracy. Many high-level decision making processes can take advantage of such redundancy to unify the content of one database with those of others. This unification of spatial objects in multiple databases is expected to extend the solution space that would otherwise be very limited or nonexistent.

Interoperability of spatial systems is a goal sought by many and, by most measures, attained by none. If systems were truly interoperable, it would be straightforward to share geographic information across software platforms and between databases collected for different purposes by different organizations. In contrast, a variety of technical, institutional, and physical barriers inhibit the fluid exchange of geographic information.

In recent years, one of the most exciting developments in information technologies is the proliferation of Internet connectivity and the popularity of World Wide Web services. Internet and Web technologies are providing the general public with a convenient way to access vast quantities of information. Almost all computer users with an Internet connection can use Web browsers to access information. These technologies and enhanced hardware and software products enable users with moderate levels of computer knowledge to establish information distribution sites and to participate actively in the evolving national information infrastructure.

This project started with the objective of creating middleware to allow users to gain access to geographic data from several different sources, using a simple object-based model. The intention was to provide the widest possible range of users with easy and inexpensive access to public GIS data. The initial concept called for the development of an interface between the user and the GIS. Initially, this interface would only provide basic data access, and should evolve in the future to support the definition and implementation of more specialized services. However, the ability to connect simultaneously to different GIS platforms has been considered important to the success of the project.

Geographical information systems (GIS) are now in common use in many bodies interested in the use of spatially-referenced data (Laurini and Thompson 1992). The new challenge concerns the extension of the use of GIS data in client–server environments, particularly through the Internet or within Intranet networks (Duda 1998; Fonseca and Davis, this volume; van den Berg et al., this volume).

Within an organization managing spatially referenced data, several types of documents are used to describe the land and its resources (for instance, topographic maps, land use maps, aerial photographs, satellite images, and so on). Managing such documents is a complex task, each document being characterized by its own content, spatial reference system, quality, sources, mode of distribution, and format. Hence, Georeferenced Digital Libraries (GDLs) can be very useful and helpful to describe the available geodocument resources in an organization. For instance, GDLs provide information about the physical location of the documents and identify who does what, when, and how. GDLs are nowadays implemented on the World Wide Web (WWW), mostly to facilitate the distribution of spatial data; these are the GDLs of interest for the present chapter although the research is not limited to the WWW.

The Earth Science Remote Access Tool (ESRAT), an enhancement to the Distributed Oceanographic Data System (DODS), is an HTTP-based client—server system that facilitates Internet access to distributed Earth science data. ESRAT addresses the great diversity of data formats used in the Earth sciences by providing a common data model with translators for the models inherent in many standard raster formats. It enables applications normally using local data in a particular format to access remote datasets in that or other supported formats.

An approach to an open infrastructure for geographic information on the Internet is presented in this chapter. This infrastructure enables data providers to publish their data independently, while enabling end users to access data from several providers simultaneously, and integrate the data locally in a geographic browser. Our goal is that an end user finds accessing geographic information in this environment as easy as if he or she were working with a state-of-the-art GIS package with all data of interest on the local computer. The key elements that are required are a common format for publishing metadata on each server, a common SQL derived query protocol, standard transfer file formats, and standard certificate-based authentication procedures, for access control and (optionally) billing. An experiment with this approach has been carried out, with three data providers in the Netherlands: the Dutch Cadastre, the municipality of Almere, and the cable-TV company Caserna. This chapter presents the major design decisions, the choices for the prototype environment, and the relationship to ongoing specification and standardization processes for geographic data. In particular the relationships with the proposed European CEN standards, and the recently accepted specifications from the OpenGIS consortium, are described.

Geospatial information has been realized as a valuable resource for more and more organizations and departments. Recently, developments of new techniques in worldwide high-speed network communications and applications make it increasingly possible for computer-based information systems to access a diversity of autonomous and remote information sources. The availability of various Internet information servers and browsing tools further promote information sharing across departmental, organizational, and national boundaries. However, since the development of the earliest recording and storage technologies in the GIS field, considerable efforts have had to be placed on data format translations and standardized data development so that applications in one organization can make use of geospatial data maintained by other organizations. This is because of the proprietary data models and representation methods of various geospatial information systems used by different communities. With the increasing removal of proprietary restrictions on geospatial data sources by providers and with the information consumer’s increasing need to import geodata, the interoperability of heterogeneous geospatial data sources must be achieved

In this last section we leave the lower-level technical aspects of interoperability, for the most part, and begin to address organization, education, and infrastructure issues and implications. As we have seen from earlier chapters, the technical challenges facing developers of interoperable GIS components are great. But just as formidable are the challenges to our institutions. Interoperability means changing paradigms not just for the technologist, but for the bureaucrat, the teacher, and the businessperson as well.

What will it take to share geographic information between real-world organizations? Despite progress in networking technology, database design, standards, and organizational wisdom over the last three decades, it’s still rare for planners or public managers to share information across organizational boundaries. it’s rare even when (as in environmental management for instance) key decision variables are linked by physical pathways (waterways, landforms, habitat) that cross jurisdictions, hierarchies, and other territorial lines. It’s rare even for geographic information, despite its cost and its potential for widespread re-use, and has remained rare even as the Internet has come of age in recent years, and as public agencies have been called to increase their efficiency and public accountability. The problem seems to be part technical, part organizational, and often peculiar to the nature of geographic information: complex in structure and interpretation, rich in meaningful interrelationships, and difficult to understand or use without special-purpose tools.

Internet marketplaces have recently been proposed as a new and interesting model to make data and computational services available to a broad public (Abel 1997; Abel et al. 1997; Günther et al. 1997). Unlike electronic commerce (on-line shopping) where services are only requested over the Internet, Internet Marketplace services are both requested and delivered through the Internet. The key idea of Internet Marketplaces is that providers make a range of services available on the Internet and customers rent them whenever necessary. Such a market model offers a range of advantages over conventional marketplaces and is attractive for both customers and providers (Gaede 1998).

Question: Why do people buy a GIS? Answer: Because their neighbor has one. Richard Newell of Smallworld Systems told this joke during his keynote speech at the 1997 Symposium on Spatial Databases—and he did not only refer to Smallworld customers. The truth behind his joke is that GIS are often greatly underutilized. Many customers use only a small fraction of the functionalities offered by their GIS. Some of them are aware of that: they simply do not care about the remaining features. Others are not: they may thus miss functionalities that are actually there and use complicated ways to reimplement them with the features they know. Yet other users may not use their GIS at all: they bought it because they thought it may help them with their problems but then found out that it does not. Some customers may not even have bothered to look: they bought the GIS andleft it in the package.

It is 2010 and geographic information (GI) is everywhere. Geographic information systems (GIS) interoperability has revolutionized the way vendors, data providers, and application developers deliver GI solutions. GI is embedded in a very wide range of information systems and decision support products from real estate sales through military applications to personal navigation. These all rely on a common global spatial data infrastructure that provides scale-independent data constantly updated. GI is available whenever and wherever it is needed. GIS have become so thoroughly interoperable that they have all but disappeared as distinct products.

The rapid development of communication and computing technology is changing the way scientific information is created, disseminated, managed, and used. Distributed computing, in particular, is increasingly being used as the foundation for scientific information management, collaboration, and publishing. This new foundation comes at a time when scientific budgets can rarely afford the creation of the large, vertically integrated scientific data centers which would otherwise be necessary to manage the explosion of information being produced today. Distributed computing is, therefore, being used to create a new scientific information infrastructure, and digital libraries are beginning to play a central role in emerging information systems.