Iteration 4 should include the following at a minimum:
The architecture may follow the 4+1 UML-based Architectural Model. At a minimum you should have a semi-detailed deployment view complete, a dialog map (or something similar that shows the flow of pages through your user interface), and a class or entity-relationship diagram for your database schema. You may include other models as you have time and see fit. An architecture document template is posted on the course wiki.
You should be making significant progress on your vertical prototype. This means that you will need to have chosen your technology stack, begun to learn the different technologies, and begun to build a prototype using those technologies. To demonstrate this, your team should demonstrate in class a working development and build environment. This should include any IDE or compiler needed, any necessary frameworks installed, and working automated build scripts (e.g. Ant or Maven). This environment may be demonstrated on a lab machine or a student laptop. In addition, you should have instructions posted on your team wiki for setting up this development and build environment.
Also called a QA Plan, this document should include details on how you intend to test (verify and validate) your system, and it should include acceptance tests for your highest priority SRS use-cases and system tests for your highest priority functional requirements. A validation plan document template is provided at course wiki.