Never locks any item

Locks an item before read/write and avoids double-locking or unlocking a free item

Always downgrades to read

Always upgrades to write

Read and write

Shared and exclusive

Unlocked and locked

Wait and wake

Invisible to reads

Available to all other transactions

Permanently read-only

Reserved by the same transaction

Invalid

Deadlocking

Conflicting

Non-conflicting

A file handle

A pointer to a page

A variable on a data item describing operation status

A transaction log record

A timeout occurs

no_of_reads(X) > 0

X is unlocked

X is read-locked

FIFO ordering of locks

Any random interleaving

Timestamp order only

Some serial order of the transactions

Shared and exclusive

Intent and schema

Strong and weak

Logical and physical

Only one write lock exists and no shared lock is allowed

Read-only access is enforced

Multiple exclusive locks are allowed

Many shared locks are allowed simultaneously

X is removed from buffer pool

Only one transaction can read X

Writes are allowed

Multiple transactions can read X, but no one may write X