Let A be a set in which the relation R is defined. Then R is said to be a symmetric relation, if (a, b) ∈ R ⇒ (b, a) ∈ R, that is, aRb ⇒ bRa for all (a, b) ∈ R. The relation R is antisymmetric, specifically for all a and b in A; if R(x, y) with x ≠ y, then R(y, x) must not hold. Or similarly, if R(x, y) and R(y, x), then x = y. Therefore, when (x,y) is in relation to R, then (y, x) is not. Here, x and y are nothing but the elements of set A.

A broadcast address is a network address used to transmit to all devices connected to a multiple-access communications network. A message sent to a broadcast address may be received by all network-attached hosts. A multicast address is used to address a specific group of devices, and a unicast address is used to address a single device. IPv4 address 255.255.255.255 is used as a limited broadcast address. Limited broadcast address 255.255.255.255 can appear as the only destination address in the IPv4 header. Limited broadcast is a type of broadcast which is limited to the Local Area Network (LAN). Routers will not forward limited broadcast IPv4 datagram packets because these broadcasts are not relevant to other networks and cause flooding everywhere in the Internet. So, the scope of limited broadcasts is limited to the Local Area Network (LAN).

Volatile memory, in contrast to non-volatile memory, is computer memory that requires power to maintain the stored information; it retains its contents while powered on but when the power is interrupted, the stored data is quickly lost. Volatile memory has several uses including as primary storage. In addition to usually being faster than forms of mass storage such as a hard disk drive, volatility can protect sensitive information, as it becomes unavailable on power-down. Most general-purpose random-access memory (RAM) is volatile

In databases and transaction processing, two-phase locking (2PL) is a concurrency control method that guarantees serializability. It is also the name of the resulting set of database transaction schedules (histories). The protocol uses locks, applied by a transaction to data, which may block (interpreted as signals to stop) other transactions from accessing the same data during the transaction's life. By the 2PL protocol, locks are applied and removed in two phases: Expanding phase: locks are acquired and no locks are released. Shrinking phase: locks are released and no locks are acquired.

In a relational database, a weak entity is an entity that cannot be uniquely identified by its attributes alone; therefore, it must use a foreign key in conjunction with its attributes to create a primary key.

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