Tables in SharePoint Content Database

Below are some of the basic tables within a content database and a very high level diagram on some of the relationships between them

Features	Table that holds information about all the activated features for each site collection or site.
Sites	Table that holds information about all the site collections for this content database.
Webs	Table that holds information about all the specific sites (webs) in each site collection.
UserInfo	Table that holds information about all the users for each site collection.
Groups	Table that holds information about all the SharePoint groups in each site collection.
Roles	Table that holds information about all the SharePoint roles (permission levels) for each site.
All Lists	Table that holds information about lists for each site.
GroupMembership	Table that holds information about all the SharePoint group members.
AllUserData	Table that holds information about all the list items for each list.
AllDocs	Table that holds information about all the documents (and all list items) for each document library and list.
RoleAssignment	Table that holds information about all the users or SharePoint groups that are assigned to roles.
Sched Subscriptions	Table that holds information about all the scheduled subscriptions (alerts) for each user.
ImmedSubscriptions	Table that holds information about all the immediate subscriptions (alerts) for each user.