Version Numbering and Negotiation

Version Number Form

The published specification version number contains three positive integers, separated by decimal points, in the form "x.y.z". The numbers "y" and "z" will never exceed 99. Each OWS specification is numbered independently. For example, WMS version has a 1.1.1, 1.3.0, etc.

Version Changes

A particular specification's version number shall be changed with each revision. The number shall increase monotonically and shall comprise no more than three integers separated by decimal points, with the first integer being the most significant. There may be gaps in the numerical sequence. Some numbers may denote experimental or interim versions. Service instance and their clients need not support all defined versions, but shall obey the negotiation rules below.

Appearance in Requests and in Service Metadata

The version number appears in at least two places: in the Capabilities XML describing a service, and in the parameter list of client requests to that service. The version number used in a client's request of a particular service instance shall be equal to a version number which that instance has declared it supports (except during negotiation as described below). A service instance may support several versions, whose values clients may discover according to the negotiation rules.

Version Number Negotiation

An OWS Client may negotiate with a Service Instance to determine a mutually agreeable specification version. Negotiation is performed using the GetCapabilities operation according to the following rules.

All Capabilities XML shall include a protocol version number. In response to a GetCapabilities request containing a version number, an OGC Web Service shall either respond with output that conforms to that version of the specification, or negotiate a mutually agreeable version if the requested version is not implemented on the server. If no version number is specified in the request, the server shall respond with the highest version it understands and label the response accordingly.

Version number negotiation occurs as follows:

• If the server implements the requested version number, the server shall send that version.
• If a version unknown to the server is requested, the server shall send the highest version less than the requested version.
• If the client request is for a version lower than any of those known to the server, then the server shall send the lowest version it knows.
• If the client does not understand the new version number sent by the server, it may either cease communicating with the server or send a new request with a new version number that the client does understand but which is less than that sent by the server (if the server had responded with a lower version).
• If the server had responded with a higher version (because the request was for a version lower than any known to the server), and the client does not understand the proposed higher version, then the client may send a new request with a version number higher than that sent by the server.

The process is repeated until a mutually understood version is reached, or until the client determines that it will not or cannot communicate with that particular server.

Example 1:Server understands versions 1,2,4,5 and 8. Client understands versions 1,3,4,6,7. Client requests version 7. Server responds with version 5. Client requests version 4. Server responds with version 4, which the client understands, and the negotiation ends successfully.

Example 2:Server understands version 4,5 and 8. Client understands version 3. Client requests version 3. Server responds with version 4. Client does not understand that version or any higher version, so negotiation fails and client ceases communication with that server.