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.

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 must 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

Negotiation is performed using the GetCapabilities operation.

All Capabilities XML must include a protocol version number. In response to a GetCapabilities request containing a version number, an OGC Web Service must 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 must 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 must send that version.
• If the client request is for an unknown version greater than the lowest version that the server understands, the server must 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 must 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, and 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 versions 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.