Query Chatter Feed Item & How the structure in Salesforce object

Salesforce admin can enable Chatter feed tracking on Salesforce object, include custom objects.
Go to Setup - App Setup - Customize - Chatter - Feed Tracking
Select object to track and tick "Enable Feed Tracking", you can select up to 20 fields.

In the background, once an object is enable for feed tracking, Salesforce will create new object end with suffix Feed (for Standard object) or _Feed (for Custom object). This is available in API version 18.0 and later.

Using SOQL, you can do this query:
Select Id, ParentId, Type, Title, Body, CommentCount, LikeCount, LinkUrl, RelatedRecordId, ContentFileName, ContentSize, ContentType From Object1__Feed
This query will return all feeds tag to Object1__c object only (see ParentId field)

Another object storing all feeds is FeedItem, this object avaiable in API version 21.0 and later.
Select Id, ParentId, Type, Title, Body, CommentCount, LikeCount, LinkUrl, RelatedRecordId, ContentFileName, ContentSize, ContentType From FeedItem Order By ParentId
This query will return all feeds tag to any objects.

See architecture below (right click image to enlarge):

Notice that objectFeed object shared the same prefix with FeedItem: 0D5

If you need the screenshot in Visio file, click here