Relational Database Design Algorithms and Further Dependencies

Full Answer Section

Attribute Preservation Condition on Decomposition

A decomposition of a relation R into relations R1 and R2 is attribute preserving if every attribute of R is also an attribute of R1 or R2. This ensures that no information is lost during the decomposition process.

Inclusion Dependencies

Inclusion dependencies represent relationships between tuples in different relations. They specify that a set of attributes in one relation must exist as a subset of attributes in another relation. For example, an inclusion dependency might state that every department number in the Department relation must appear in the Employee relation.

DKNF as the Ultimate Normal Form

DKNF is considered the ultimate normal form because it eliminates all redundancies and anomalies in a relation. A relation is in DKNF if every non-trivial functional dependency X -> A implies that X is a superkey. In simpler terms, every non-trivial functional dependency must involve a candidate key.

Relational Database Design Algorithms and Further Dependencies

Primary and Secondary Storage

• Primary Storage: This is high-speed storage, such as RAM, used to store data that is currently being accessed by the CPU. It is volatile, meaning data is lost when the power is turned off.
• Secondary Storage: This is slower, non-volatile storage, such as hard disks or SSDs, used to store data persistently. It can be accessed by the CPU but is typically slower than primary storage.

RAID Levels

RAID (Redundant Array of Independent Disks) is a storage technology that combines multiple disk drives into a single logical unit. ¹ Different RAID levels offer different trade-offs between performance, redundancy, and cost:  

• RAID 0: Stripping data across multiple disks for improved performance.
• RAID 1: Mirroring data across multiple disks for redundancy.
• RAID 5: Block-level striping with distributed parity for data recovery.
• RAID 6: Block-level striping with dual parity for increased fault tolerance.
• RAID 10: Combination of mirroring and striping for both performance and redundancy.

Buffer Manager Function

A buffer manager is a component of a database management system (DBMS) that manages the allocation of memory buffers to store data pages. When a request for data is made:

1. Buffer Request: The DBMS requests a buffer from the buffer manager.
2. Buffer Allocation: The buffer manager allocates a free buffer to the request.
3. Disk I/O: If the required data is not in the buffer pool, the buffer manager initiates a disk I/O operation to fetch the data.
4. Data Transfer: Once the data is retrieved, it's transferred to the allocated buffer.
5. Data Access: The requesting process can now access the data from the buffer.
6. Buffer Replacement: When the buffer pool is full, the buffer manager uses a replacement policy (e.g., Least Recently Used, First-In-First-Out) to evict a buffer.

By managing the buffer pool, the buffer manager can significantly improve the performance of database operations.

Sample Answer

Closure of Functional Dependencies

The closure of a set of functional dependencies, denoted as F+, is the set of all functional dependencies that logically follow from F. In other words, it's the complete set of dependencies that hold in the relation.

Example: Consider a relation R(A, B, C) with the following functional dependencies:

• A -> B
• B -> C

The closure of F, F+, would include:

• A -> C (derived from A -> B and B -> C)