There are many different types of traceability matrix - the one that comes to mind is a requirements traceability matrix in which you illustrate using tables your testcase to requirement coverage. For each test case that covers a requirement you indicate the coverage with a mark in the cell linking the testcase to the requirement.
Life should NOT be a trip to the grave with the intention of arriving safely in an cool and well preserved body, but rather to skid in, chocolate in one hand, beer in the other, body wrecked, totally worn out and screaming WOO HOO what a ride!
As corklad said, there are many different types, mostly as he says based on relating what is being tested to test cases.
This can be useful for identifying coverage, for audit trail of what has been tested and as a look-up table for regression testing. You can add to it to serve many other uses.
Originally posted by spgan: How about vertical direction? Example, relationship among test cases?
<font size="2" face="Verdana, Arial, Helvetica">Agreed: bi-directional says you can go from one to the other and back from the other to the one.
There is also the notion of horizontal and vertical direction (where people often interchange both - me included [img]images/icons/confused.gif[/img] ). I use always use the V-Model to define vertical - horizontal. So vertical is between documents at different levels. Example: a requirements document is used as input for a functional design (vertical traceability).
Horizontal is between documents at the same level. Example: a functional design that is used as input for developing system test cases (horizontal).
Both vertical and horizontal traceability can be bi-directional.