GetCapabilities Response |
In WMS special situations that conform to OGC standards, XML responses must be valid according to the DTD (XML Document Type Definition). DTD represents required and optional contents in the responses, and formulation of content formats.
Capabilities XML documents on the server completely refer to DTD documents, rather than main parts of URL. DTD documents must be positioned in completely qualified and usable URL, so as to be indexed by XML verification software.
WMS Capabilities XML mainly contains two components of Service and Capability.
Contents of the <Service> element in WMS Capabilities XML represent general service metadata, and this element provides an integral description of server general metadata. This data contains Name, Title and Online Resource URL elements, as well as some optional contents: Abstract, KeywordList, ContactInformation, Fees and AccessConstraints elements.
Table 1 Elements of general service metadata
| Element name | Description |
| Name | Name of WMS service. |
| Title |
Service titles. Brief descriptions of the server, depending on the service providers, distinguishable from other servers. |
| Abstract |
Service abstracts. Provides more descriptions about server information. |
| KeywordList |
Keywords. Server as a whole can help directory searches. |
| OnlineResource |
Online resources. Provides website references for service providers. Other OnlineResource elements are URL prefixes of each operation. |
| ContactInformation |
Contact information, including service providers' names, addresses, telephones, faxes, emails, etc. Service metadata should contain this element. |
| Fees |
Fees. This element can be ignored if the server does not use fees. If having used this element, "none" (case insensitive) means free, such as "<Fees>none</Fees>". |
| AccessConstraints |
Access constraints. This element can be ignored if the server does not use access constraints. If having used this element, "none" (case insensitive) means no access constraints, such as "<AccessConstraints>none</AccessConstraints>". If using this element and contents of this element have no accurate grammar definition, the client can display user information and behavior contents. |
Contents in the <Capability> element represents requests supported by server examples (GetCapabilities, GetMap or GetFeatureInfo), output formats provided by each kind of operation, as well as URL prefixes of each operation. XML DTD contains placeholders of DCP (Distributed Computing Platforms), and other HTTP request methods. However, only HTTP GET is defined as a basic WMS operation at present.
Ignorable service provider-specific elements can be contained in the <Capability> element. SLD (Styled Layer Descriptor, map style table) WMS also contains the <UserDefinedSymbolization> element and URL requested by HTTP POST.
Layer and Style are the most important parts in WMS Capabilities XML documents.
Each usable map is listed in Capabilities XML documents through the <Layer> element. A parent layer can contain any number of child layers.
Map server must contain at least one <Layer> element in each provided map.
Name, Title and Keywords of Layer/Style are optional at present.
The <Layer> element can enclose child elements providing metadata about the Layer.
Table 2 Layer properties
| Elements | O/M /Optional |
Description |
| Title |
R |
A Title is required for all layers; it is a human-readable string for presentation in a menu. The Title is not inherited by child Layers. |
| Name |
O |
Name If, and only if, a layer has a <Name>, then it is a map layer that can be requested by using that Name in the LAYERS parameter of a GetMap request. A Client shall not attempt to request a layer that has a Title but no Name. A server shall throw an exception (code="LayerNotDefined") if an invalid layer is requested. The Name is not inherited by child Layers. |
| Abstract |
O |
Abstract Abstract is a narrative description of the map layer. The Abstract is not inherited by child Layers. |
| KeywordList |
O |
KeywordList KeywordList contains zero or more <Keyword> to aid in catalog searches. The KeywordList is not inherited by child Layers. |
| Style |
O |
Style Zero or more Styles may be advertised for a Layer or collection of layers using <Style> elements, each of which shall have <Name> and <Title> elements. The style's Name is used in the Map request STYLES parameter. A Style may contain several other elements in the Capabilities XML DTD. In particular, <Abstract> provides a narrative description while <LegendURL> contains the location of an image of a map legend appropriate to the enclosing Style. A <Format> element in LegendURL indicates the MIME type of the logo image, and the attributes width and height state the size of the image in pixels. Style declarations are inherited by child Layers. A child shall not redefine a Style with the same Name as one inherited from a parent. A child may define a new Style with a new Name that is not available for the parent Layer. |
| SRS |
R |
SRS (Spatial Reference System) Every Layer is available in one or more spatial reference systems(or in an undefined SRS.SRS declarations are inherited by child Layers. The root <Layer> element shall include a sequence of zero or more SRS elements listing all SRSes that are common to all subsidiary layers. SuperMap iServer currently supports POSC (EPSG:4326) format only. Value is EPSG:0 if published as planar coordinate system. |
| LatLonBoundingBox |
O |
LatLonBoundingBox Every Layer shall have exactly one <LatLonBoundingBox> element that is either stated explicitly or inherited from a parent Layer. LatLonBoundingBox states the minimum bounding rectangle of the map data in the EPSG:4326 geographic coordinate system. The LatLonBoundingBox attributes minx, miny, maxx, maxy indicate the edges of an enclosing rectangle in decimal degrees LatLonBoundingBox purposes is to facilitate geographic searches without requiring coordinate transformations by the search engine. |
| BoundingBox |
R |
BoundingBox Layers may have zero or more <BoundingBox> elements that are either stated explicitly or inherited from a parent Layer. < BoundingBox> elements contain the following attributes:
BoundingBox metadata indicates coordinate extents of layers, and the request parameter BBOX indicates map extents. BBOX area does not necessarily intersect with, or contain, or be contained by BoundingBox area. A Layer inherits any BoundingBox values defined by its parents. |
| ScaleHint |
O |
Layers may include a <ScaleHint> element that suggests minimum and maximum scales for which it is appropriate to display this layer. ScaleHint is inherited by child Layers. A ScaleHint declaration in the child replaces the any declaration inherited from the parent. |
| Dimension |
O |
Used for multi-dimensional data. Dimension declarations are inherited from parent Layers. Any new Dimension declarations in the child are added to the list inherited from the parent. A child shall not redefine a Dimension with the same name attribute as one that was inherited. |
| Extent |
O |
Used for multi-dimensional data. Extent declarations are inherited from parent Layers. Any Extent declarations in the child with the same name attribute as one inherited from the parent replaces the value declared by the parent. A Layer shall not declare an Extent unless a Dimension with the same name has been declared or inherited earlier in the Capabilities XML. |
| MetadataURL |
O |
MetadataURL A Map Server should use one or more <MetadataURL> elements to offer detailed, standardized metadata about the data underneath a particular layer. The type attribute indicates the standard to which the metadata complies. Two types are defined at present: the value 'TC211' refers to [ISO 19115]; the value 'FGDC' refers to [FGDC-STD-001-1988]. The MetadataURL element shall not be used to reference metadata in a nonstandardized metadata format; see DataURL instead. The enclosed <Format> element indicates the file format MIME type of the metadata record. MetadataURL elements are not inherited by child Layers. |
| Attribution |
O |
The optional <Attribution> element provides a way to identify the source of the map data used in a Layer or collection of Layers. <OnlineResource> states the data provider's URL. <Title> is a human-readable string naming the data provider. <LogoURL> is the URL of a logo image. A <Format> element in LogoURL indicates the MIME type of the logo image. The attributes <width> and <height> state the size of the image in pixels. The Attribution element is inherited by child layers. |
| Identifier and AuthorityURL |
O |
A Map Server may use zero or more <Identifier> elements to list ID numbers or labels defined by a particular Authority. |
| FeatureListURL |
O |
FeatureListURL A Map Server may use a <FeatureListURL> element to point to a list of the features represented in a Layer. FeatureListURL is not inherited by child layers. |
| DataURL |
O |
A Map Server may use DataURL to offer more information about the data represented by a particular layer. DataURL is not inherited by child layers. |
A <Layer> may have zero or more of the following XML attributes: queryable, cascaded, opaque, noSubsets, fixedWidth, fixedHeight.All of these attributes are optional and default to 0, in keeping with WMS 1.0.0.Each of these attributes can be inherited or replaced by subsidiary layers.
Table 3 Layer Attributes
| Attribute | Allowed Values | Meaning (0 is default value) |
| queryable | 0, 1 |
0: not queryable. 1: queryable. |
| cascaded | 0, positive integer |
0: layer has not been retransmitted by a Cascading Map Server. n: layer has been retransmitted n times. |
| opaque | 0, 1 |
0: map data represents vector features that probably do not completely fill space. 1: map data are mostly or completely opaque. |
| noSubsets | 0, 1 |
0: WMS can map a subset of the full bounding box. 1: WMS can only map the entire bounding box. |
| fixedWidth | 0, positive integer |
0: WMS can resize map to arbitrary width. nonzero: map has a fixed width that cannot be changed by the WMS. |
| fixedHeight | 0, positive integer |
0: WMS can resize map to arbitrary height. nonzero: map has a fixed height that cannot be changed by the WMS. |
The MIME type of data returned by the GetCapabilities operation is application/vnd.ogc.wms_xml, which is the xml document in essence.
The example usage of response contents of GetCapabilities Request exampleis as follows: