What is decomposition | What is Database life cycle in DBMS ?

•  DECOMPOSITION :-

    Decomposition is breaking up a relational schema into smaller relations such that each of the attributes is present in at least one of the new relations, and has a more optimized design. The underlying goal is to remove data redundancy.

Following tables 5.5, 5.6 and 5.7 illustrates how the decomposition would work:-

• Properties of Decomposition  :- 

       (i) Lossless and Lossy Decompositions 

      (ii) Dependency-Preserving Decompositions 

1.  Lossless and Lossy Decompositions :-

                        Decomposition of a relation R into relations X and Y is lossless if no infomation from ginarelation is lost after the decomposition. In other words. the original relation can te construct ed back from the decomposed relations and no extra rows of infornation are ded as data to the resuling rows.

       2. Dependency-Preserving Decompositions :-

               Dcomposition of a relation R into relatons A ant Y 1s depemeney-preserving who the fumctional dependencies (FDs) that hold on A AMa t epariety, when put togeth oresxnd to alt the FDs that erist in the closure ot functional dependency F" (F\ U E hold on the original relation, R.

               It follows from the above that given a dependeney preserving decomposition, if we s can check all the constraints against the decompused table only, we need not check it again original table.  

• DATABASE LIFE CYCLE (DBLC) :-
  

          The database life eycle includes database creation and resourte alBocation. managing the database schema and data. and pertorming backup and ecovery tasks. Database administrators and applicaticon developers perform the database lite cycle tasks. The Database Life Cycle (DBLC) contains six phases, as shown in the following figure:

1. Database initial study
   
   
2. Database design 
   
   
3. Implementation and loading
   
   
4.  Testing and evaluation
   
   
5.  Operation 
   
   
6.  Maintenance and evolution
   
   

• Database Initial Study: In the Databuse initial study, the designer must examine the current system's operation within the company and determine how and why the curret system fails. The overall purpose of the database initial study is to:   

            (a) Analyze the company situation 

            (b) Define problems and constraints 

            (c) Detine objectives 

            (d) Define scope and boundaries

1. Analyze the Company Situation: The company situation describes the general conditions in which a company operates, its organizational structure, and its mission To analyze the company situation, the database designer must discover what the company's operational components are, how they function, and how they interact. 
   
   
2.  Define Problems and Constraints: The designer has both formal and informai sources of information. The process of defining problems might initially appear to be unstructured. Company end users are often unable to describe precisely the larger scope of company operations or to identify the real problems encountered during company operations
   
   
3.  Define Objectives: A proposed database system must be designed to solve at least the major problems identified during the problem discovery process. In any case, the database designer must begin to address the following questions: What is the proposed system's initial objective? Will the system interface with other existing or future systems in the company? Will the system share the data with other systems or users?
   
   
4. Define Scope and Boundaries: The designer must recognize the existence of two sets of limits: scope and boundaries. The system's cope defines the extent of the according to operational requirements. Will the database design the organization, one or more departments within organization, or one or more functions of a type single department? Knowing the scope helps in the required data structures. The proposed system is also subject to known as boundaries .

• Implementation and Loading:-

                 The output of the database design phase is a ser of instructions specifying the creation of tables, attributes, domains, views, indexes, securi constraints, and storage and performance guidelines. In this phase,. you actually implement al these design specifications.

1. Install the DBMS: This step is required only when a new dedicated instance of the DBMS is necessary for the system. The DBMS may be installed on a new server or it may be installed on existing servers. One current trend is called virtualization. Virtualization is a technique that ereates logical representations of computing resources that are independent of the underlying physical computing resources.
   
   
2. Create the Databases: In most modem relational DBMS(s), a new database implementation requires the creation of special storage-related constructs to hold the end-user tables. The constructs usually include the storage group (or file groups), the table spaces, and the tables.
   
   
3. Load or Convert the Data: After the database has been created, the data must be loaded into the database tables. Typically. the data will have to be migrated from the prior version of the system. Often, data to be included in the system must be aggregated from multiple sources. Data may have to be imported from other relational databases. non reiational databases, flat files, legacy systems, or even manual paper-and-pencil system .

• Testing and Evaluation:-

                In the design phase. decisions were made to ensure integrity. security. pertomance, and and recoverability of the database. During implementation loading, these plans were put into place. In testing and evaluation, the DBA tests and fine-tunes the database to ensure that it performs as expected.

1. Test the Database: During this step. the DBA lests the database to ensure that it mainiains the integrity and security or the data. Data integrity is enforced by the DBMS through the proper use of primary and roreign key rules. In database Physical testing vou must check security allows Password security, Access nghts, Data encryption etc.
   
   
2.  Fine-Tune the Database: Although performance can be difficult to evaluate because there are no standards for database performance measures, it is typically one of the performance requirements on the database. Many factors can impact the database's performance on various tasks. Environmental tactors, such as the hardware and software environment in which the database exists, can nave a significant impact on database factors in database implemention Different systems will place different performance .
   
   

• Evaluate the Database and Its Applieation Programs:-
                   As the database and the systein must also be evaluated from a more programs Testing and evaluation of the individual components should conclude in a plication approach. der system tests to ensure that all of the components interact properly ariey he users. To ensure that to meet the data contained in the databuse are protected against vaiety of broader system the needs of loss, backup and recovery plans are tested.
  
  
• Operation:-

                      Once the database has passed the evaluation stage, it is considered to be operational. nal, At that point. the database, its management, its users, and its application constitute a complete information system. The beginning of the operational phase ograns con invariably starts the process of system evolution. 

• Maintenance and Evolution: 
                       The database administrator must be prepared to perterm routine maintenance activities within the database. Some of the maintenance activities required periodic include: 

1.  Preventive maintenance (Backup).
   
   
2.  Corrective maintenance (Recovery). 
   
   
3. Adaptive maintenance (enhancing performance , adding entities and attributes, and so on).
   
   
4.  Assignment of access permissions and their maintenance for new and old users.