Category: Lists

Collections of attributes may be grouped together in a single FME feature using an attribute list. An attribute list element is just like any other attribute except that it contains an integer index enclosed in braces {} as part of its name.

By convention, the first element of a list has an index of 0.

For example, if a feature has these attributes on it:

    ids{0}  50

    ids{1}  45

    ids{2}  10

We would say that the feature has an unstructured list named "ids{}" with three elements. In FME Workbench, the list would be shown as part of a transformer output using its unqualified list name ids{}.  

If a feature has these attributes on it:

    overlaps{0}.direction  -1

    overlaps{0}.line_id    50

    overlaps{1}.direction  1

    overlaps{1}.line_id    22

    overlaps{2}.direction  1

    overlaps{2}.line_id    40

    overlaps{3}.direction  -1

    overlaps{3}.line_id    12

We would say that the feature has an structured list named "overlaps{}" with four elements. In FME Workbench, the list would be shown as part of a transformer output by using two unqualified names – overlaps{}.direction and overlaps{}.line_id.

Unqualified list names remind us that there are a number of actual attribute values present on the feature. However, it is not possible to directly access values from an unqualified list name. Instead, these names can be used as parameters to the various transformers that operate on lists. As well, by right-clicking on any unqualified list, a number of its elements may be exposed and from then on be accessed directly. Such attributes are called qualified list elements.