Fundamentals of computer science tutorial (FCST)

Timestamp based concurrency control  algorithm                Timestamp   : -    A monotonically increasing variable (integer) indicating the age of an operation or a transaction.    A larger timestamp value indicates a more recent event or operation. Timestamp based algorithm uses timestamp to serialize the execution of concurrent transactions       Basic Timestamp Ordering   1.    Transaction T issues a write_item(X) operation: If read_TS(X) > TS(T) or if write_TS(X) > TS(T), then an younger transaction has already read the data item so abort and roll-back T and reject the operation. If the condition in part (a) does not exist, then execute write_item(X) of T and set write_TS(X) to TS(T). 2.    Transaction T issues a read_item(X) operation: If write_TS(X) > TS(T), then an younger transaction has already written to the data item so abort and roll-back T and reject the operation. If write_TS(X)  £  TS(T), then execute read_item(X) of T and set read_TS

Cardinality/Binary relationship Cardinality/Binary relationship defines the numerical attributes of the relationship between two entities or entity sets. Types of  Cardinality/ Binary relationship Cardinality/ Binary relationship are four types. now discuss all types of Binary relation ship. One to one relationship  : - When a single instance of an entity is associated with a single instance of another entity then it is called one to one relationship. For example : - a person has only one passport and a passport is given to one person. One to many relationship   : - When a single instance of an entity is associated with more than one instance of another entity then it is called one to many relationship. For example: - One customer can placed many orders but an order can’t be placed by many customers. Many to One relationship : - When more than one instance of an entity is associated with single instance of another entity then it is c

        Normalization in DBMS Normalization  is a process that “improves” a database design by generating relations that are of higher normal forms. The  objective  of normalization:  “ to create relations where every dependency is on the key, the whole key, and nothing but the key ”. We discuss four normal forms: first, second, third, and Boyce-Codd normal forms 1NF, 2NF, 3NF, and BCNF There is a sequence to normal forms: 1NF is considered the weakest, 2NF is stronger than 1NF, 3NF is stronger than 2NF, and BCNF is considered the strongest Also, any relation that is in BCNF, is in 3NF; any relation in 3NF is in 2NF; and any relation in 2NF is in 1NF. a relation in BCNF, is also in 3NF a relation in 3NF is also in 2NF a relation in 2NF is also in 1NF We consider a relation in BCNF to be fully normalized.  The benefit of higher normal forms is that update semantics for the affected data are simplified. This means that applications re

Client server architecture (explains the client server architecture of DBMS/explains three tier architecture of DBMS)      Client server architecture is an architectural deployment style that describes separation of functionality into layers with each segment being tier that can be located on a physically separate computer. A client server architecture separate its tier from each other based on the complexity of user and how they used the data present in the database. It is the most widely used architecture to design a DBMS.   Client server architecture are divided into three part. Three part are A)   Database tier   B)   Application(middle) tier   C)   Presentations (user) tier A. Database tier : -  At this tier database resides along with its query processing languages. We also have the relation that define the data and their constrains at this level.         B. Application (middle) tier : -  At this tier reside the application server and program that ac

Two-Phase Locking Techniques Locking is an operation which secures (a) permission to Read or (b) permission to write a data item for a transaction.  Example:  Lock  (X).  Data item X is locked in behalf of the requesting transaction.  Unlocking  is an operation which removes these permissions from the data item.  Example:  Unlock  (X).  Data item X is made available to all other transactions.  Lock and Unlock are Atomic operations Two-Phase Locking Techniques: Essential components 1)  Two locks modes (a) shared (read) and (b) exclusive (write). Shared mode:  shared lock (X).  More than one transaction can apply share lock on X for reading its value but no write lock can be applied on X by any other transaction. Exclusive mode:  Write lock (X).  Only one write lock on X can exist at any time and no shared lock can be applied by any other transaction on X. Conflict matrix 2) Lock Manager:  Managing locks on data items    Lock table: Lock manager uses it to store th