Database systems assignment 1
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Database systems address several issues related to data storage and management: 1. Data redundancy and inconsistency are eliminated through database normalization which prevents duplicate data and ensures data remains consistent. 2. Difficulty in accessing data is resolved by providing application programs and interfaces to access and manage data through a database management system. 3. Data isolation and scattering across different files and formats is addressed by collecting all data into a centralized database.
Database systems assignment 1
- 1. ASSIGNMENT 1 JKUAT Course: Database Systems Date: 16th July 2016
- 2. 1. Explain the following issues related to data storage and management and show how database systems address them. Give examples. (15 Marks) Data redundancy and inconsistency Redundancy refers to unnecessarily duplicated data that is not needed or no longer needed. This maybe a field repeated in one or more tables in a database. A good example is when customer data are duplicated and attached with each product bought. Applying database normalization prevents redundancy and makes the best possible usage of storage. Inconsistency is a situation where copies of the same data exist and not all of them are updated. A good example is a case where someone's address is on a system severaltimes, and then their address changes,but it is only updated in some of those places, then the person will have both their old and new address on the system. Data inconsistency is likely to occur when there is data redundancy and therefore by normalization of a database we eliminate a possible occurrence of inconsistent data. Difficulty in accessing data Difficulty in accessing data arises whenever there is no application program for a specific task. A database management system allows access to the data in a database and consists of a set of interrelated data together with a set of programs to access those data. Data isolation This problem arises due to the scattering of data in various files with various formats. Due to the above disadvantages of the earlier data processing system, the necessity for an effective data processing system arises. Only at that time the concept of DBMS emerges for the rescue of a large number of organizations. Data integrity Data integrity means that the data values in the data base should be accurate in the sense that the value must satisfy some rules. Relational database systems use constraints to achieve data integrity. The three constraints are; Entity Integrity: This is concerned with the concept of primary keys. The rule states that every table must have its own primary key and that each has to be unique and not null, ReferentialIntegrity: This is the concept of foreign keys. The rule states that the foreign key value can be in two states. The first state is that the foreign key value would refer to a primary key value of another table, or it can be null. Being null could simply mean that there are no relationships, or that the relationship is unknown, and the domain Integrity: This states that all columns in a relational database are in a defined domain. Atomicity Atomicity is a feature of databases systems dictating where a transaction must be all-or-nothing. That is, the transaction must either fully happen, or not happen at all. It must not complete partially. Atomicity is usually achieved by complex mechanisms such as journaling or logging, or via operating-system calls.
- 3. Concurrent access Concurrent access means multiple users are allowed to update the data simultaneously in a database. Database systems use concurrency controlconcept to address conflicts with the simultaneous accessing or altering of data that can occur with a multi-user system. Concurrency control, when applied to a DBMS, is meant to coordinate simultaneous transactions while preserving data integrity. Concurrency control is achieved using database locks. Data security Data security means prevention of data accession by unauthorized users. Database systems address this issue by providing roles which define what a particular database user is allowed to access. An example, in a banking system, payroll personnel need to see only that part of the database that has information about the various bank employees. They do not need access to information about customer accounts. 2. What is the difference between Procedural DMLs and Declarative DMLs. Give examples (5 Marks) The prime difference between these two data manipulation languages is that procedural languages specify how the output of a DML statement is to be obtained, while declarative DMLs describe only what output is to be obtained. Typically, procedural languages treat records individually, where as declarative languages operate on sets of records. References Lecture Notes Nick (2014). The Data Manipulation Language (DML). Retrieved from http://www.winstudent.com/the-data-manipulation-language-dml/ Ambler, Scott (2006). Introduction to Concurrency Control. Retrived from http://www.agiledata.org/essays/concurrencyControl.html