What is an example of sociological and agency representationin congress?

US Congress
Agency Representation
Sociological Representation

That's a rather vague question. I would call sociological representation, members of Congress primarily focused on agenda driven issues like gay rights or areas of interest to specific ethnic groups. For example the people in Congress representing San Francisco would be interested in gay rights issues because they have sizeable numbers of gays in their constituency.

If by "agency representation" you are referring to government agencies, many members of Congress have interest in issues involving specific agencies, often because they serve on oversight committees for them. For example, Senator Judd Gregg from New Hampshire is very knowledgeable on financial issues and serves on the Senate Banking Committee.

If, by "agency representation," you mean the legislator is acting like an "agent" for a certain group however, that sounds more like the relationship between Congress and lobbyists. Most anybody in Congress could be used as an example for that. :-)