Drupal 6 modules typically defined their own tables, had their own code to maintain them and then used nodeapi to hook into the system. Or, defined node types but still maintained their own tables. In Drupal 7 instead you should just create fields, instance them on node types you want to work with. Instead of altering a form directly you can write a widget. Display your data with a formatter. Don't worry about data storage, field API handles that for you. And then there is the EntityFieldQuery class to help with finding things.
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