Types of relationship tables

Relationship tables can be designed to suit a variety of types of relationships, including one way links, and links associating concept, task and reference topics.

There are many different ways that you can organise relationship tables. The most common are:
source and target
The source column lists the topics in which a link will be included, and the target column lists the topics that the source will be linked to ("from source, to target"). Target topics do not have links back to the source topic.
task, concept, and reference
Topics are organised into columns by information type. Each topic in a cell will be linked to all other topics that are in other cells in the same row. Topics in the same cell will not be linked to each other unless that cell's collection-type attribute is set to family.
task, concept, reference, and external
Topics are organised into columns by information type, with an extra column for link targets that are external to the ditamap collection. Each topic in a cell will be linked to all other topics that are in other cells in the same row, and all URLs listed in the external cell in the same row. Topics in the same cell will not be linked to each other unless that cell's collection-type attribute is set to family.

Some people have found that a four column arrangement of sourceonly task, targetonly concept, targetonly task, and targetonly reference is effective.

The arrangement of the reltable is defined by the following attributes in the relcolspec or relcell elements of the table:
linking
defines the rules by which links are generated
type
defines the information type (concept, task, reference, specialised)
scope
defines whether the related information is external to the collection (typically, a Web resource)

A setting in the relcolspec element will cascade down to the relcell element.

You can also choose to have a number of relationship tables of different designs in the same ditamap. You can use the reltable's title attribute to label the different reltables in a map; this title is not used in any output, so it is only an aid to authors.