Common request parameters |
The version number parameter (VERSION) indicates the version number of the protocol, the format of the version number, and the version negotiation. See Version Number and Negotiation .
The request parameter (REQUEST) indicates which service operation to invoke. The value of this parameter must be one of the operation names provided by the server.
The Format parameter (FORMAT) specifies the output format in response to an operation.
WMS may only provide a subset of the appropriate formats for this type of operation. The server must detail the formats it supports in its service metadata and must accept requests for operations on any of the formats it enumerates. The server may choose to provide a new format that was not previously available in other instances. And does not require the client to accept or otherwise process the unknown format. If the request contains a format that is not provided by a server, the server uses the default format in response to the operation if the default format is predefined. If the default format is not defined, the server throws a service exception (code "InvalidFormat").
The client accepts only a subset of the format that corresponds to the type of operation. If the client and server do not support any mutually consistent format, the client makes a determination, either to interrupt communication with the server, or to find other service providers that can convert the format, or to allow the user to choose another deployment method.
The format is detailed in the service metadata and in the operation request using the MIME type. Each operation has a unique list of supported formats. Some formats can be provided by several operations and replicated in the required list.
The exception parameter (EXCEPTIONS) States the format in which the error is reported. (See Service Exception )
WMS allows for selective extension of capabilities and operations. When additional functionality or specialization is required, extensions can be defined in the body of the information. Universal clients are not required or expected to use extension modules. Extend the capabilities or operations, if necessary, through a summary of the instances provided in the entity's service metadata schema The < _ Extended Capabilities > element or the < ExtendedCapabiltites > element. The extension capability provides additional metadata about the service, enabling optional new parameters to be included or excluded from the operation request. Extended operations allow the use of predefined additional operations.
The server must respond legitimately to an operation defined by the OGC standard even if a parameter used by the extended capability is missing or incorrect, or if a parameter unknown to the server is provided (for example, if a default value is defined, the server must respond with a default value for the extended capability).
The service providers must choose their extension names carefully to avoid conflicts with standard metadata fields, parameters, and operations.