GMLFeatureComposer

Input features containing attributes and geometries appropriate to particular GML feature types.

Serialized GML documents are output via this port.

Features with duplicate gml_id values within a group are output via this port.

Features with gml_parent_id values referring to non-existing gml_id(s) are output via this port.

Features with no corresponding GML feature types.

Setting this parameter to Yes allows a single GML document to be composed from many features. The document structure, the nesting of features in the document, may be controlled via the gml_id and gml_parent_id attributes. Each feature within a group must have a unique gml_id. Features with duplicate ids are send to the DuplicateIds port. Features with gml_parent_id(s) pointing to non-existing parents are sent to the Orphans port

If you do not select Group By attributes, then all features fall into the same group.

When you select Group By attributes, this transformer will compose a GML document, based on the selection in the Group By parameter. Each group of features that have the same values for the Group By attributes will be processed independently of other groups.

Process At End (Blocking): This is the default behavior. Processing will only occur in this transformer once all input is present.

Process When Group Changes (Advanced): This transformer will process input groups in order. Changes of the value of the Group By parameter on the input stream will trigger processing on the currently accumulating group. This may improve overall speed (particularly with multiple, equally-sized groups), but could cause undesired behavior if input groups are not truly ordered.

Considerations for Using Group By

There are two typical reasons for using Process When Group Changes (Advanced) . The first is incoming data that is intended to be processed in groups (and is already so ordered). In this case, the structure dictates Group By usage - not performance considerations.

The second possible reason is potential performance gains.

Performance gains are most likely when the data is already sorted (or read using a SQL ORDER BY statement) since less work is required of FME. If the data needs ordering, it can be sorted in the workspace (though the added processing overhead may negate any gains).

Sorting becomes more difficult according to the number of data streams. Multiple streams of data could be almost impossible to sort into the correct order, since all features matching a Group By value need to arrive before any features (of any feature type or dataset) belonging to the next group. In this case, using Group By with Process At End (Blocking) may be the equivalent and simpler approach.

Note: Multiple feature types and features from multiple datasets will not generally naturally occur in the correct order.

As with many scenarios, testing different approaches in your workspace with your data is the only definitive way to identify performance gains.

Use this parameter to specify the XML Schema .xsd file, implementing the existing GML application schema. The parameter is required by the transformer to configure itself so that it may serialize to the various GML feature types found in the schema.

Optionally specifies the attribute whose value holds the GML feature type. The FME feature type will be used if this attribute is absent.

The attribute specified by this clause must exist in the input features and its value must equal to one of the GML feature types determined from the parsed application schemas.

The attribute to hold the GML output.

The encoding for the GML output.

This parameter specifies a set of XML namespace declarations that may be used to augment and/or overwrite the namespace declarations in the GML output. The legal values for this parameter are whitespace-separated XML namespace declarations as they would appear in an XML element.

Determines if FME writes the Geometries as a gml:Polygon or a gml:PolygonPatch. The default value is 'no', which prints out gml:Surface geometries. If 'yes', FME creates the geometry as a gml:Polygon in the output.

This parameter allows the user to overwrite the CRS value that is written in the GML geometry’s srsName attribute.

This parameter is required when the GML srsName parameter is used. It specifies the axis order for a coordinate tuple in a GML <pos> or <posList> element. The valid values for this parameter are “1,2”, “2,1”, “1,2,3” and “2,1,3”. There is no default value.

The parameter specifies if the GML output should be pretty-printed with indentation.

This parameter specifies the size of a single indentation.

By default, the tab character is used for pretty printing, use this parameter to replace the tabs with spaces.

This parameter specifies how embedded GML objects (those containing a gml:id), that are not geometries should be mapped.

By default, these embedded objects are mapped into FME attributes.

If the parameter is set to Geometries, the embedded objects are mapped into FME Geometries, and the embedded object properties are loaded into geometric traits. In turn, nested embedded objects are mapped into nested aggregate geometries.

If the parameter is set to Feature Types, the embedded objects will be mapped into separate FME feature types, and these feature types will have an additional gml_parent_id attribute whose value refers back to its parent feature.

Specifies whether the default and optional GML feature properties, name and description, should be read.

The GML writer will automatically substitute concrete elements that are substitutable for abstract GML properties. Some GML formats declare properties that are not abstract but are nevertheless head of substitution groups.

Selecting this parameter instructs the GML writer to also generate FME attributes for member elements belonging to the substitution group headed by these non-abstract GML properties.

When this option is selected, the FME feature type and attribute names will include the XML Namespace prefixes used in the GML application schema. The prefix will be separated from the names via an underscore.

Specifies whether GML properties that are defined as a complex type with complex content (that is, those that have embedded children elements) should be mapped as nested list attributes within FME features.

If the value is set to XML Fragments, then the complex properties with complex content are mapped as XML fragments.

Some complex properties, such as those that are recursively defined, cannot be mapped as nested lists. These complex properties will always be mapped as XML fragments, regardless of the setting for this parameter.

This optional parameter can control the depth of nested list attributes.