Version numbering and negotiation

Version number format

The version number is expressed in three positive integers, separated by decimal points, in the form of "x.y.z", and the numbers "y"and "Z" cannot exceed 99. For example, WFS Versions are 1.0.0, 2.0.0, etc.

Appearance of version number

The version number appears in at least two places, in the Capabilities XML document used to describe the service and in the client's request parameters.

Version number negotiation

The client-side and server-side version number negotiation is done through the GetCapabilities operation.

All Capability XML must include the protocol version number, and in order to respond to a GetCapabilities request that includes the version number, WFS must respond with the same version as the request.

The version number requested by the client should match the version number supported by the server, otherwise, the most recent matching principle should be followed:

• If the server implements the requested version, the server must return the version number.
• If the client requests an unknown version number that is higher than minimum version number that the server understands, the server must send a maximum version number that is lower than requested version.
• If the client requests a version lower than any of the server's versions, the server must send a minimum version number that it understands.
• If the client does not understand the new version number sent by the server, the client can either stop interacting with the server or send a request with a new version that the client understands, but that is less than version number previously returned by the server.
• If the server has responded to a higher version (because the client requested a lower version than whatever the server understands), but the client does not understand this version, the client can send a new version number with a higher version number than one returned by the server.

The process is repeated until both sides reach an agreement or the client cancels the communication with the server.

Example 1. The server understands versions 1, 2, 4, 5, and 8. Client understands versions 1, 3, 4, 6, 7. The client first requests version 7, and the server responds to version 5. The client then requests version 4, and the server responds to version 4. The client and the server reach an agreement.

Example 2. Server Understanding Versions 4, 5, 8. Client understands version 3. The client first requests version 3. The server responds with version 4. The client does not understand this version or any later version. The client stops communicating with the server.