Ok, maybe i am not seeing the entire picture or something like that, however i kinda require a brainstorm.

Therefore the purpose is to create a webapp (HTML5, CSS, Javascript) that needs to explore a 250mb database with no web connection, so.. yes the database needs to be around the client side.

Hard part here's, this Application needs to focus on an ipod device or apple iphone without web connection. (A preliminary link with download the Application is alright), LocalStorage includes a 5mb limit, couchDB could be great given that they come with an webapp easily utilized by Javascript (privacy concerns don't matter at this time), so i am virtually from ideas....

Does anybody see an alternate, or solution with the objective?

You cannot store a 250MB database in 5MB of storage.

Possible work-arounds:

  1. Knowing regarding your data, you are able to write a specialized compression formula.
  2. Store merely a subset from the data offline which you're thinking that user uses. When they need other data, they will have to connect.
  3. Don't include images, sounds, videos, etc. within the offline data, but include all of the text. 5MB holds lots of text, but not so many pictures and graphics.

I believe you need to use the various tools best fitting to do the job... which appears to become a client-application-job. This is a small tutorial using a database (sqlite) around the apple iphone and you ought to have the ability to use every other embeddable database availalable for that apple iphone/iPad, too.

Sqlite on the iPhone Tutorial

If you're really instructed to use HTML5 and also the web widget items you pointed out above you wil have the choice to embed a browser window right into a native application and react for url changes or publish/get messages.