Question: I must develop a simple web application to produce reports. I have a single table "contract" and i must return very simple aggregated values : number of documents produced in a time range, average number of pages for documents and so on . The table gets filled by a batch application, users will have roles that will allow them to see only a part of the reports (if they may be called so ). 

My purpose is :

1. develop a class, which generates the so called reports, opened to future extension (adding new methods to generate new reports for different roles must be easy )
2. decouple the web graphic interface from the database access

I'm evaluating various patterns : decorator, visitor, ... but being the return data so simple i cannot evaluate which apply or even if its the case to use one. Moreover i must do it i less than 5 days. It can be done if i make a so called "smart gui" but as told at point 1, i don't want to get troubles when new roles or method will be added.

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thank you for your answers. 
I'm sorry, i realize i haven't provided too much infos. I live in a Dilbert world. at the moment i've got the following info : db will be oracle (the concrete db doesn't exist yet) , so no EF, maybe linqtodataset (but i'm new to linq). About new features of the application,due to pravious experiences, the only thing i wish is not to be obliged to propagate changes over the whole application, even if it's simple. that are the reasons i've thougth to design patterns (note i've said "if it's the case" in my question) .
I'll KISS it and then will refactor it if needed , as suggested by ladislav mrnka, but i still appreciate any suggestion on how to keep opened to extension the data gathering class

Answer: 
KISS - keep it simple and stupid. You have five days. Create working application and if you have time refactor it to some better solution.
How about you use strategy pattern for the retrieving data? And use interfaces like following to keep it extendable at all times.

* IReportFilter: Report filter/criteria set
* IReportParams: Gets report parameters
* IReportData: Gets the report data in a result set
* IReportFormat: Report formatting
* IReportRender: Renders the report

Just thinking out loud.