Found 338 Articles for DBMS

Let’s see the stages of database system life cycle (DDLC) and their facts using tabular form −Stage of Database system development LifecycleExample of FactsExample of Documentation ProducedDatabase PlanningAims and objectives of database projects.Mission statements and objectives.System IdentificationDescription of major user views (Job roles, business application areas).Definition of scope and boundary of database system, definition of user views to be supported.Requirements Collection and AnalysisRequirements of user views, system specifications, including performance and security requirements.User requirement specification, system specification.Database designUser’s responses to checking the logical database design, functionality provided by target DBMS.Logical database design, data dictionary, physical database design.Application DesignUsers’ response to ... Read More

A schedule has view-serializability if it is viewed as equivalent to a serial schedule. A schedule is view serializable if the following three rules are satisfied −Rule 1 − If Ti reads data initially, after this Tj writes the same data, in the given schedule. This sequence must be followed in the transaction combination (read write operation).Rule 2 − If Ti writes data initially, after this Tj reads the same data, in the given schedule. This sequence must be followed in the transaction combination (write read operation).Rule 3 − If Ti writes data, after this Tj writes the data finally. ... Read More

PL/SQL is oracle’s procedural language extension to SQL. PL/SQL allows you to mix SQL statements with procedural statements like IF statements. Looping structure etc, PL/SQL is the superset of SQL. It uses SQL for data retrieval and manipulation and uses its own statement for data processing.Pl/SQL program units are generally categorized as follows −Anonymous blockThis is a PL/SQL block that appears within your application. In many applications PL/SQL blocks can appear where SQL statements can appear. Such blocks are called Anonymous blocks.Stored proceduresThis is a PL/SQL block that is stored in the database with a name. Application programs are executing ... Read More

The different phases of database development life cycle (DDLC) in the Database Management System (DBMS) are explained below −Requirement analysis.Database design.Evaluation and selection.Logical database design.Physical database design.Implementation.Data loading.Testing and performance tuning.Operation.Maintenance.Now, let us understand these phases one by one.Requirement AnalysisThe most important step in implementing a database system is to find out what is needed i.e what type of a database is required for the business organization, daily volume of data, how much data needs to be stored in the master files etc.In order to collect all this information, a database analyst spends a lot of time within the business ... Read More

In a transaction, a data item which we want to read or write should first be locked before any read or write operation. After the operation is over, the transaction unlocks the data item so that other transactions can lock that same data item for their use.ExampleLet us see how locking mechanisms help us to create error free schedules.An erroneous schedule is as follows −Here t2 reads A, before A is modified in T1. This will result in inconsistency.Now we use locking mechanism in the above schedule which is shown below −Until T1 performs Unlock(A) T2 cannot access A. So, ... Read More

Two schedules are said to be conflict equivalent if the order of any two conflicting operations are the same in both the schedules.Also, a concurrent schedule S is conflict equivalent to a serial schedule S’, if we can obtain S’ out of S by swapping the order of execution of non-conflicting instructions.Example 1Even if the schedule S1 keeps the database in the consistent state, we cannot convert it into a serial schedule and hence we conclude that the schedule is not conflict equivalent to any of the serial schedules.So, instead of considering only the read and write operation, we will ... Read More

Conflict serializability orders any conflicting operations in the same way as some serial execution. A pair of operations is said to conflict if they operate on the same data item and one of them is a write operation.That meansReadi(x) readj(x) - non conflict   read-read operationReadi(x) writej(x) - conflict         read-write operation.Writei(x) readj(x) - conflic      t write-read operation.Writei(x) writej(x) - conflict      write-write operation.Where I and j denote two different transactions Ti and Tj.Precedence graphIt is used to check conflict serializability.The steps to check conflict serializability are as follows −For each transaction T, put ... Read More

A schedule is serialized if it is equivalent to a serial schedule. A concurrent schedule must ensure it is the same as if executed serially means one after another. It refers to the sequence of actions such as read, write, abort, commit are performed in a serial manner.ExampleLet’s take two transactions T1 and T2, If both transactions are performed without interfering each other then it is called as serial schedule, it can be represented as follows −T1T2READ1(A)WRITE1(A)READ1(B)C1READ2(B)WRITE2(B)READ2(B)C2Non serial schedule − When a transaction is overlapped between the transaction T1 and T2.ExampleConsider the following example −T1T2READ1(A)WRITE1(A)READ2(B)WRITE2(B)READ1(B)WRITE1(B)READ1(B)Types of serializabilityThere are two types ... Read More

A transaction must satisfy the ACID properties of DBMS, namelyAtomicity − Execute all or none transaction.Consistency − The DB should be consistent before and after transaction execution.Isolation − Transaction must be executed in isolated form.Durability − Roll backing should always be possible in Case of any failure.A schedule is defined as an execution sequence of transactions. A schedule maintains the order of the operation in each individual transaction. A schedule is the arrangement of transaction operations. A schedule may contain a set of transactions.We already know that a transaction is a set of operations. To run transactions concurrently, we arrange ... Read More

Query is a question or requesting information. Query language is a language which is used to retrieve information from a database.Query language is divided into two types −Procedural languageNon-procedural languageProcedural languageInformation is retrieved from the database by specifying the sequence of operations to be performed.For Example − Relational algebra.Structure Query language (SQL) is based on relational algebra.Relational algebra consists of a set of operations that take one or two relations as an input and produces a new relation as output.Types of Relational Algebra operationsThe different types of relational algebra operations are as follows −Select operationProject operationRename operationUnion operationIntersection operationDifference operationCartesian ... Read More