what services can be offered?

What services can be offered?
A service is any application that is accessed by means of a URL for example Google. The output of a service may be XML, HTML an image etc. And in some cases the output of a service may be used as input to other services or as a query for the portal. Examples of integration of services in the portal are:
*a Google image search with an author name as search parameter
*annotation of records
In some cases the result of a link to a service is a web page ,in other cases the results can be integrated in the presentation (like an image or XML with a known schema). It may also possible to process the output of a service with a known HTML layout and make the results available to the portal. It is obvious that there are not very many restrictions in what type of services can potentially be offered to the user. Besides that a lot of intelligence can be added to the portal in dealing with these services in an appropriate way. For example some services might be accessed automatically based on other criteria than only the presence of a metadata field