Interoperability is "the ability of a system or a product to work with other systems or products without special effort on the part of the customer" (OGC, 2004). This means that two or more systems or components are able to transmit or exchange information through a common system and to use the information that has been exchanged. Another definition is: "The capability to communicate, execute programs, or transfer data among various functional units in a manner that requires the user to have little or no knowledge of the unique characteristics of those units” (ISO 19118).
When systems are interoperable, it gives the user the ability to:
- find what need,
- access it,
- understand and use it,
- have goods and services responsive to their needs
There are two types of interoperability (OGC, 2004):
- syntactic (or technical): when two or more systems are capable of communicating and exchanging data, they are exhibiting syntactic interoperability. Specified data formats and communication protocols are fundamental. In general, XML or SQL standards provide syntactic interoperability. Syntactical interoperability is required for any attempts of further interoperability.
- semantic: Beyond the ability of two or more computer systems to exchange information, semantic interoperability is the ability to automatically interpret the information exchanged meaningfully and accurately in order to produce useful results as defined by the end users of both systems. To achieve semantic interoperability, both sides must refer to a common information exchange reference model. The content of the information exchange requests are unambiguously defined: what is sent is the same as what is understood (i.e. explaining why INSPIRE is producing data specifications).
Services play an essential role in the use of Spatial Data Infrastructures. The selection, presentation, transformation and integration of data are all done by services. A service is a component with a standardized task that communicates by a standardized interface. A simple service is the presentation of a spatial dataset on a standardized way. Services can also be combined to form a new service. This is called service chaining. For the description of a service the ISO 19119 standard is used (service metadata). The OGC has been active in the formulation of implementation specifications for services.