Views of Data in Query Evaluation (cont)
Representing database objects during query execution:
-
DB (handle on an authorised/opened database)
-
Rel (handle on an opened relation)
-
Page (memory buffer to hold contents of disk block)
-
Tuple (memory holding data values from one tuple)
Addressing in DBMSs:
-
PageID = FileID+Offset ... identifies a block of data
- where
Offset gives location of block within file
-
TupleID = PageID+Index ... identifies a single tuple
- where
Index gives location of tuple within page
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