51.   What is Domain-Key Normal Form?

A relation is said to be in DKNF if all constraints and dependencies that should hold on the the constraint can be enforced by simply enforcing the domain constraint and key constraint on the relation.

52.   What are partial, alternate,, artificial, compound and natural key?

Partial Key:

It is a set of attributes that can uniquely identify weak entities and that are related to same owner entity. It is sometime called as Discriminator.

Alternate Key:

            All Candidate Keys excluding the Primary Key are known as Alternate Keys.

Artificial Key:

 If no obvious key, either stand alone or compound is available, then the last resort is to simply create a key, by assigning a unique number to each record or occurrence. Then this is known as developing an artificial key.

            Compound Key:

                 If no single data element uniquely identifies occurrences within a construct, then combining multiple elements to create a unique identifier for the construct is known as creating a compound key.

            Natural Key:

            When one of the data elements stored within a construct is utilized as the primary key, then it is called the natural key.

53.   What is indexing and what are the different kinds of indexing?

Indexing is a technique for determining how quickly specific data can be found.

Types:

Ø       Binary search style indexing

Ø       B-Tree indexing

Ø       Inverted list indexing

Ø       Memory resident table

Ø       Table indexing

54.   What is system catalog or catalog relation? How is better known as?

A RDBMS maintains a description of all the data that it contains, information about every relation and index that it contains. This information is stored in a collection of relations maintained by the system called metadata. It is also called data dictionary.

55.   What is meant by query optimization?

The phase that identifies an efficient execution plan for evaluating a query that has the least estimated cost is referred to as query optimization.

56.   What is join dependency and inclusion dependency?

Join Dependency:

                        A Join dependency is generalization of Multivalued dependency.A JD {R1, R2, ..., Rn} is said to hold over a relation R if R1, R2, R3, ..., Rn is a lossless-join decomposition of R . There is no set of sound and complete inference rules for JD.

            Inclusion Dependency:

                        An Inclusion Dependency is a statement of the form that some columns of a relation are contained in other columns. A foreign key constraint is an example of inclusion dependency.

57.   What is durability in DBMS?

Once the DBMS informs the user that a transaction has successfully completed, its effects should persist even if the system crashes before all its changes are reflected on disk. This property is called durability.

58.   What do you mean by atomicity and aggregation?

Atomicity:

Either all actions are carried out or none are. Users should not have to worry about the effect of incomplete transactions. DBMS ensures this by undoing the actions of incomplete transactions.

            Aggregation:

            A concept which is used to model a relationship between a collection of entities and relationships. It is used when we need to express a relationship among relationships.

59.   What is a Phantom Deadlock?

In distributed deadlock detection, the delay in propagating local information might cause the deadlock detection algorithms to identify deadlocks that do not really exist. Such situations are called phantom deadlocks and they lead to unnecessary aborts.

60.   What is a checkpoint and When does it occur?

A Checkpoint is like a snapshot of the DBMS state. By taking checkpoints, the DBMS can reduce the amount of work to be done during restart in the event of subsequent crashes.

61.   What are the different phases of transaction?

Different phases are

Ø       Analysis phase

Ø       Redo Phase

Ø       Undo phase

62.   What do you mean by flat file database?

It is a database in which there are no programs or user access languages. It has no cross-file capabilities but is user-friendly and provides user-interface management.

63.   What is "transparent DBMS"?

It is one, which keeps its Physical Structure hidden from user.

64.   Brief theory of Network, Hierarchical schemas and their properties

Network schema uses a graph data structure to organize records example for such a database management system is CTCG while a hierarchical schema uses a tree data structure example for such a system is IMS.

65.   What is a query?

            A query with respect to DBMS relates to user commands that are used to interact with a data base. The query language can be classified into data definition language and data manipulation language.

66.   What do you mean by Correlated subquery?

            Subqueries, or nested queries, are used to bring back a set of rows to be used by the parent query. Depending on how the subquery is written, it can be executed once for the parent query or it can be executed once for each row returned by the parent query. If the subquery is executed for each row of the parent, this is called a correlated subquery.

A correlated subquery can be easily identified if it contains any references to the parent subquery columns in its WHERE clause. Columns from the subquery cannot be referenced anywhere else in the parent query. The following example demonstrates a non-correlated subquery.

 E.g. Select * From CUST Where '10/03/1990' IN (Select ODATE From ORDER Where CUST.CNUM = ORDER.CNUM)

67.   What are the primitive operations common to all record management systems?

Addition, deletion and modification.

68.   Name the buffer in which all the commands that are typed in are stored

            ‘Edit’ Buffer

69.   What are the unary operations in Relational Algebra?

            PROJECTION and SELECTION.

70.   Are the resulting relations of PRODUCT and JOIN operation the same?

            No.

            PRODUCT: Concatenation of every row in one relation with every row in another.

            JOIN: Concatenation of rows from one relation and related rows from another.

71.   What is RDBMS KERNEL?

            Two important pieces of RDBMS architecture are the kernel, which is the software, and the data dictionary, which consists of the system-level data structures used by the kernel to manage the database

            You might think of an RDBMS as an operating system (or set of subsystems), designed specifically for controlling data access; its primary functions are storing, retrieving, and securing data. An RDBMS maintains its own list of authorized users and their associated privileges; manages memory caches and paging; controls locking for concurrent resource usage; dispatches and schedules user requests; and manages space usage within its table-space structures

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72.   Name the sub-systems of a RDBMS

            I/O, Security, Language Processing, Process Control, Storage Management, Logging and Recovery, Distribution Control, Transaction Control, Memory Management, Lock Management

73.   Which part of the RDBMS takes care of the data dictionary? How

            Data dictionary is a set of tables and database objects that is stored in a special area of the database and maintained exclusively by the kernel.

74.   What is the job of the information stored in data-dictionary?

            The information in the data dictionary validates the existence of the objects, provides access to them, and maps the actual physical storage location.

75.   Not only RDBMS takes care of locating data it also

            determines an optimal access path to store or retrieve the data

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