Should user interfaces be included in the class diagram and sequence diagram?

I have a project and I'm required to produce the class and sequence diagram. It is a procurement website. My only problem is that I don't know how to associate the web pages (user interfaces) to these diagrams. If they are not needed what is the right way for me to include it in the diagrams because from a book I read there are "UserInterface" classes, so another question, what should be inside of these UI classes.Can someone give me an example. Thanks!

There are several levels of abstraction for UI modelling.

• Use cases and state machines. These diagrams are made in human terms.
• Planning on the server/page/frame level. Here UML deployment and component diagrams are useful.
• Planning of the content of UI, defining elements and functonalities and connections between them WITHOUT choosing the concrete components. No standard for this, extremely important, stage. Use diagrams that you like. Class ones are usable, but in not standard reading.
• Planning of the content of screen elements WITH choice of the UI components (frames, buttons and so on) and connecting functionalities to them. On this level you can use class and sequence diagrams.
• Drawings of the planned screenshots. For this level there are no UML diagrams. And a common standard doesn't exist.

These levels require MANY diagrams. The lower the level, the more diagrams it needs. Putting user interfacES into one class diagram is possible for a minuscule project, but you can't say it SHOULD be done so.