Questions on user defined data types

Hi there:

I want to ask the if I could define an object like type in postgresql, it may be better to illustrate with actual examples.

Background information:

1, I would like to pack group of data into 1 entry of in a table.

2, The table consist some financial product information including names, public data and etc.

3, Each product need to be valued, and the packed entry contains all the assumptions (interest rate, etc.) to perform valuation calculation of the products.

Furthermore, for company management purpose, the packed data would have the following properties:

1, Elements of the entry can be easily queried, using SQL;

2, Change of element value is not allowed by simple update, only using pre-complied "methods" functions can update them;

3, Changes using methods functions would be recorded into a specified sub-object called "LOG", which record down update information including update times and etc.

I am asking if this could be realized and if yes, how should I do it.

Thank you so much ~~

Shore