| Sequential |
Sequentially (forward only)
The sequential
record value of each record can be obtained and used as a key |
SEQUENTIAL backward or forward
KEYED using
the sequential record value
Positioning by key followed by sequential
either backward or forward |
New records at end only
Access can be
sequential or KEYED
Record deletion allowed |
Advantages Simple
fast creation
Uses For uses where data is
primarily accessed sequentially |
| Keyed |
Either sequentially or randomly by key |
KEYED by specifying key of record
SEQUENTIAL
backward or forward in order of any index
Positioning by key followed
by sequential reading either backward or forward |
KEYED specifying a key
SEQUENTIAL following
positioning by key
Record deletion allowed
Record insertion
allowed |
Advantages Complete
access and updating
Uses For uses where access
is related to key |
| Direct |
Sequentially starting from slot 1
KEYED
specifying number of slot
Positioning by key followed by sequential
writes |
KEYED specifying numbers as key
Sequential
forward or backward omitting empty records |
Sequentially starting at a specified slot
and continuing with next slot
Keyed specifying numbers as key
Record deletion allowed
Record insertion into empty slots allowed |
Advantages Speedy
access to record by number
Disadvantages Structure
tied to numbering sequences
Uses For
use where records are accessed by number |