UML Distilled by Martin Fowler is the ideal book to start with, i would also recommend Object-Oriented Systems Analysis and Design by Simon Bennett. These two would provide a definitive guide. As well as this there are numerous UML cheat sheets online including
Try learning the Entity Relationship Model : http://en.wikipedia.org/wiki/Entity-relationship_model
And also the Unified Modeling Language : http://en.wikipedia.org/wiki/Unified_Modeling_Language
Here is one book by Korth: http://www.db-book.com/ for starting DBMS. Have a look at the ER-Model chapter.
For UML have a look at : http://www.amazon.com/UML-Distilled-Standard-Modeling-Language/dp/020165783X?tag=particculturf-20
UML Distilled by Martin Fowler is the ideal book to start with, i would also recommend Object-Oriented Systems Analysis and Design by Simon Bennett. These two would provide a definitive guide. As well as this there are numerous UML cheat sheets online including
UML Quick Reference Guide
UML Reference Card
UML Cheatsheet
I use sequence diagrams to document the flow from page to page (including Ajax requests). Within a page, activity diagrams are often useful
For an excellent, short, and readable introduction to the use of UML, see UML Distilled