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2. OGIS Overview

2.1 What Will OGIS Do?

Developers building systems with OGIS interfaces will create middleware, componentware, and applications that can handle a full range of geodata types and geoprocessing functions. Users of these systems will be able to share a potentially huge networked data space in which all geodata conforms to a generic data model, even though the data may have been produced at different times by unrelated groups using different production systems for different purposes and may in fact still reside under the primary control of the systems used in their production. Legacy geodata will be brought into conformance by encapsulation and will be accessed via software with OGIS interfaces, as shown in Figure 2-1.

Figure 2-1 OGIS-compliant interfaces will enable geoprocessing interoperability in wide area network applications, local area network applications, and desktop applications.

OGIS will, for example, enable a user of a standard desktop PC running a low-cost OGIS-compliant mapping application to query a remote data server on the Internet, probably through a simple graphical selection technique in the mapping application. The remote data server will store geodata in a commercial, general purpose relational database management system (RDBMS) configured with an OGIS interface. The data delivered by the server might have been created years earlier on a Genasys, Intergraph MGEª, or ESRI ARC/INFOª system. Or it might be a set of plain corporate RDBMS records whose street addresses fall within a region defined graphically in the query that the user executed through the mapping application. Some information might be lost in this transfer, due to the limitations of the client mapping application, but the server and the mapping application could cooperate to inform the user, cursorily or verbosely, about this information loss.

Clients will also be able to request geoprocessing services from remote servers. The low-cost mapping application, for example, could download a toolbar of GIS functions by which the user would control a sophisticated and powerful remote GIS server.

The Open Geodata Interoperability Specification (OGIS) provides a framework for software developers to create software that enables their users to access and process geographic data from a variety of sources across a generic computing interface within an open information technology foundation.

"a framework for software developers" means OGIS is a detailed software specification based on a comprehensive, common (i.e., formed by industry consensus for general use) plan for interoperable geoprocessing.

"access and process" means, in this context, that geodata users can query remote databases and control remote processing resources, and also take advantage of other distributed computing technologies such as software delivered to the user's local environment from a remote environment for temporary use. It also means that geoprocessing can take advantage of interapplication sharing of "applets" in componentware, or "compound document" environments.

"from a variety of sources" means that users will have access to data acquired in a variety of ways and stored in a wide variety of relational and nonrelational databases.

"across a generic computing interface" means that OGIS interfaces provide reliable communication between otherwise disparate software resources that are equipped to use these interfaces. That is, software that can send or receive data through its OGIS interface can interoperate with other software that has an OGIS interface.

"within an open information technology environment" means that OGIS enables geoprocessing to take place outside of the closed environment of monolithic GIS, remote sensing, and AM/FM systems that control and restrict database, user interface, network, and data manipulation functions. The dominant computing paradigm is moving away from closed systems to open systems, away from isolated systems to systems that interoperate in real time, away from tightly wrapped independent applications to application environments equipped with software components that interoperate to provide more flexible capabilities for the user.

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2.2 How will OGIS Benefit Developers, Managers, and Users?

Global computing is a rapidly emerging reality. The Internet and other computer networks are providing access to burgeoning sources of data and services for millions of users. The advantages of using such technology are obvious to most users of geodata and geoprocessing resources. Large organizations need to integrate geodata and geoprocessing resources across wide area networks, and so do small organizations. Within desktop environments, differing geodata and geoprocessing resources must be integrated to enable useful work. OGIS facilitates integration in both the network environment and the desktop "compound document" environment. Within a decade, scores of millions of miniature GPS units will be embedded in vehicles, mobile telephones, personal digital assistants, personal locators, farming and earthmoving equipment, and shipping containers. Specialized implementations of OGIS will contribute to the utility of these devices.

Application developers, information managers, and end users -all of whom are part of the global computing revolution -benefit from OGIS compliant software in these ways:

The Application Developer can more easily and more flexibly:

The Information Manager has greater flexibility to:

End users are the ultimate beneficiaries, receiving:

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2.3 What is the Scope of OGIS?OGIS scope

OGIS addresses two out of the three basic aspects of the problem of accessing and using geographic data from a variety of diverse sources:

Getting connected: OGIS does not address the realm of the Distributed Computing Platform (DCP) which enables applications to interact with each other even though they are on different computers. DCPs address issues of networking, communicating between different computer systems from different manufacturers, security, distributed data storage, and other client/server platform issues. The OGIS specification does not duplicate any of the efforts being made in this area. These issues continue to be addressed by other technology providers, and OGIS will continue to track this progress and depend on this foundation. OGIS is not limited to a particular DCP.

Getting service: This is the realm of OGIS, enabling applications to interact with other applications that manage, deliver and process geodata. It addresses how to provide a service; how to request a service; and how to determine whether a request is a request for data, a request for an operation on data, or both. It defines a set of standard data types and operations on those data types, thus providing a common framework for interoperability among providers and consumers of geographic data. And it provides the services that facilitate data sharing between different Information Communities (sets of users with different meanings, semantics, and syntax for geodata and spatial processing).

These capabilities depend on the definition of a common data model for the transfer of geographic information, and the definition of the behavior of operations on that data. To preserve the vast investment in existing geographic information and geographic information systems, and to ensure the opportunity to introduce new methods for managing and manipulating geographic information, OGIS stops short of defining how to store data or how to process it.

Understanding the results: This is the realm of individuals or groups that have a common interest in the meaning accorded data. They provide the framework for interpreting the data - its intended meaning, its accuracy, its level of certification, and so on. The definition of the content of these data falls outside the scope of the OGIS specification; however, the OGIS specification needs to provide a framework by which this information can be shared between and among providers and consumers.

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2.4 An Open Model for Geodata, Services, and Information Sharing

The OGIS framework has three main parts, summarized here and described in detail in the remaining chapters:

The Open Geodata Model part of the OGIS Specification Model defines a general and common set of basic geographic information types that can be used to model the geodata needs of more specific application domains, using object-based and/or conventional programming methods.

The OGIS Services Model part of the OGIS Specification Model defines the set of services needed to 1) access and process the geographic types defined in the Open Geodata Model and 2) provide capabilities to share geodata within communities of users who use a common set of geographic feature definitions and translate between different communities of users that use different sets of geographic feature definitions.

The Information Communities Model employs the Open Geodata Model and the OGIS Services Model in a scheme that establishes:

  • 1) A way for a community of geodata producers and users who already share a common set of geographic feature definitions to efficiently and effectively maintain these definitions and to catalog and share datasets conforming to these definitions.
  • 2) An efficient and optimally accurate way for different communities of geodata users and producers to share geodata despite their dissimilar sets of geographic feature definitions. For example, civil engineers, geologists, and agronomists may seek to share soils data despite the fact that they characterize soil types differently according to their different professional objectives. The Information Communities Model defines a scheme for automated translation between different geographic feature lexicons.

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    3. OGIS Project Technical Goals and Objectives

    3.1 Introduction

    The OGIS Project Technical Committee intends to achieve the technical goals and objectives described in this chapter by offering application developers the overall OGIS Specification Model and a detailed, directly implementable specification of its parts. The architectural objectives explained in this chapter are presented from the viewpoint of application developers who will implement OGIS directly to create OGIS-compliant geoprocessing applications, application development tools, middleware, software components, encapsulations of existing tools and databases, etc.

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    3.2 Technical Goals

    The OGIS Project's Goal: Specify technology that will enable an application developer to use any geodata and any geoprocessing function or process available on "the net" within a single environment and a single work flow.

    This goal is further articulated by the following definitions:

    The "application developer" is the primary user of the OGIS geodata types and geoprocessing services, accessing these resources via standard Application Programming Interfaces (API).

    "Geodata" includes any digital representations of natural or human-made Earth features or Earth phenomena defined by spatial and/or temporal coordinate systems.

    A "geospatial function or process" is any function or process which handles or operates on geodata.

    "The net" means the full extent of the network which is accessible from any information system.

    "Within a single environment and a single work flow" means that the user's work flow extends across the net, accessing geoprocessing services and other geoprocessing applications in a distributed, cooperative way to accomplish some application-specific work objective. This is in contrast to current systems which force the user to interrupt work flow to accomplish tedious data integration tasks, OGIS-based software will present the user with only those tasks actually required to perform the work objective.

    OGIS addresses the technology barriers that exist 1) within the geoprocessing community and 2) between the geoprocessing community and other segments of the information technology industry.

    Figure 3-1 OGIS removes the barriers that have confined geoprocessing in isolated, monolithic systems.

    Figure 3-1 illustrates the progress that OGIS facilitates. Traditional geoprocessing systems have been called "monolithic," "stovepipe," or "closed" systems. That is, they were developed during a time when openness was unattainable because a rich environment of standard system services had not yet evolved. Early geoprocessing systems had to develop proprietary schemes for functions such as display, user interface, data communications, and data storage. Until very recently, these holdovers from the era of self-enclosed, proprietary systems have dominated the world of geoprocessing.

    Organizations using traditional geoprocessing applications and other traditional information technology typically have several distinct monolithic applications, often platform dependent, with limited ability to share computing and data resources. Often there are redundant functions and databases between applications. Training requirements are excessive because of the diversity of user interfaces. These applications lack the facilities to easily accommodate new methods and data types as they become available. These shortcomings greatly limit the potential of geoprocessing technology.

    In contrast to traditional geoprocessing technology, the open geoprocessing capabilities defined within OGIS establish a common technology foundation on which the software industry can build geoprocessing applications and software components that are:

  • Interoperable - OGIS provides standard interfaces to geodata and geoprocessing services. These interfaces support, in stand-alone systems and across networks: geodata access, geodata interchange, distributed client-server geoprocessing operations, and distributed peer-to-peer geoprocessing operations.
  • Supportive of Information Communities - OGIS optimizes data sharing within a community of users and producers who share a common geographic feature lexicon and between sets of users and producers whose geographic feature lexicons do not coincide.
  • Ubiquitous - OGIS provides the means for all information technology applications to readily take advantage of OGIS geodata and geoprocessing services through standard interfaces and protocols.
  • Reliable - Distributed geoprocessing requires a high level of manageability and integrity. OGIS provides a technology framework that will support Open GIS Certification.
  • Easy to use - OGIS-based software will employ logical and consistent rules and procedures for the use of geodata and geoprocessing services. Unnecessary geodata and geoprocessing complexity are "hidden" from the application developer.
  • Portable - OGIS is independent of software environment, hardware platform and network.
  • Cooperative - OGIS supports shared computing and shared data resources. OGIS technology can be easily combined with other information technology.
  • Scalable - OGIS-based software will often consist of "plug-and-play" geoprocessing software components which are configurable for any geoprocessing application or standard computing environment, regardless of size of database.
  • Extensible - OGIS can assimilate new geoprocessing software and geodata types, and can accommodate new technologies upon which OGIS is dependent, such as Distributed Computing Platforms, as they become available.
  • Compatible - OGIS preserves users' investments in legacy data and software by providing the means to seamlessly integrate, in a fashion which is transparent to the user, existing geoprocessing software and geodata and related information technology with OGIS-compliant geoprocessing applications. Also, OGIS is compatible and does not overlap with supporting information technology, particularly Distributed Computing Platforms and database management systems.
  • Implementable - The most important goal is that the technologies specified in OGIS must be implementable.

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    3.3 How to Achieve the Technical Goals

    The OGIS Project Technical Committee process works to unify the disparate views of the geoprocessing community with respect to the goals and objectives of OGIS. Separate working groups address

    The Technical Committee process is detailed in Appendix B. In addition to meeting and writing parts of the specification, many Technical Committee participants are involved in software development activities that involve OGIS. Their experience feeds into the specification process. Members of the Technical Committee and Management Committee are also involved in national and international standards efforts, so OGIS both reflects and influences other standards activity.

    3.3.1 Objectives for Unification of Geodata Models

    A unifying geodata model should:

    3.3.2 Objectives for Unification of Geoprocessing Services

    Specified OGIS service interfaces define the behavior of geoprocessing software services which access, interchange, manage, manipulate and present geodata. These service interfaces should:

    3.3.3 Objectives for Support of Inter-Community Resource Sharing

    OGIS will specify capabilities that support the integration of information and processing resources between communities of geodata users. Specifically, it should provide:

    In the next chapters we see how all these requirements are met by the Open Geodata Model, the OGIS Services Model, and Information Communities Model.

    Copyright © 1996, Open GIS Consortium, Inc.