Abstract
Usability is of a growing importance. It is crucial for the acceptance of software systems nowadays.
Software usability in its classical sense is mainly the property of the user interface of a system. Usable interface should have at least three properties: it must be easily understood and remembered and not too laborious in use.
We show that in SOA systems called confederation the first two properties should have the interfaces of constituent application services. It is a precondition for the usability of user system interface.
The properties are crucially important for the software engineering aspects of confederations (scalability, modifiability, reuse of existing systems, stability) as well as for their functions, e.g. for business processes (flexibility, on-line modifiability, etc.). We discuss some standardization issues.