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Data Environments

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Chapter I

Define each of the following terms in your own word

a) Database
b) DBMS
c) Metadata

a) Database (Crucial Concept): A database is essentially a means of storage and retrieval of items of data. The data is usually either numerical or textual, although other data forms can be accommodated.

A database is a collection of data held logically and with a purpose. Is designed and organized in such manner that it can be accessed later on for different purposes. For example we need to access our Database to update some information from it or just to extract it. Most of the businesses need a DB. They need to retrieve data in its complete form for further analysis or different objectives. Databases are needed to store our data being ready and available when required.

b) DBMS (Crucial Concept): The DBMS would be responsible for all database activities (storage, retrieval, indexing, etc) and also be responsible for keeping a detailed description of the data being held.

DBMS is a program that helps users to communicate with the Operating System through an interface in order to access the data from a Database in a friendly way and as soon as possible. It allows users to store retrieve and update information quick and productive. DBMS handle to recover the database in case of system error and needs to have an organized system for security issues.


c) Metadata – Data that Describes Data

Metadata it’s all about data being held in a Database. There is no clear definition about this. I prefer to say that is the data or information contained in a DB.

Chapter II

List and briefly describe each of the four main components of a modern database system.

The four main components of a DB system are:

a) Data
b) Hardware
c) Software
d) Users

a) Data – Information that is stored in the DB. Some of the systems can have single-user in which at most one user can access the DB at any given time or multi-user in which many users can access the DB at the same time. Data in a DB system can be Integrated or Shared. Integrated is when a DB contains more files with any redundancy between those files partly eliminated. Shared is when data in the DB can be shared between users in the same time for different purposes.
b) Hardware – The main hardware parts are: - storage volumes, where is included all hardware types that are used to hold the stored data. Mostly are used magnetic disks.
- Processor and RAM memory
which are used to support the execution of the database software
c) Software – The “thing” that make connection between physical
DB (the data physically stored) and the users of the system. It’s the main “piece of the game” who “speaks” with the computer in the name of users. Database Manager or DBMS which is also known provide all facilities for the user to retrieve, update, or remove data from the DB. DBMS is the most important software component from a DB system but is not the only one. There are other development tools, design helps and the transaction manager.
d) Users – There are 3 types of users. Programmers which are responsible for designing and coding a DB application in a programming language; DB Administrator who will control the DB after is created and End Users who interact with the system. End Users use an interface to communicate with the system for input data or retrieve it but they cannot write more functions in the DB system

Chapter III

Briefly explain the major functions performed by the DBMS.

The major Functions are: - Data storage, retrieval and update
- Creation and maintenance of the data
dictionary
- Managing the facilities for sharing the
database
- Backup and recovery
- Security

The DBMS must allow users to store retrieve and update information in a friendly way. Users need to input their data into the Database easily without knowing about the structure of the DBMS or how it was designed. When a user needs to find or update a specific data from a Database that should be quick and easy. The GUI is designed in such way to be helpful for the user. Users are not supposed to be concerned about internal structure of the Database.
The data dictionary is a ‘database about the database’ according to definition. It contains information about the Database which is used. It has information about the tables and columns, the name of them; describes characteristics of data, relationships between them and which program access data. DBMS need to create and maintain (updating, replacing, etc, data when is needed) this Data Dictionary for good functionality.
DBMS has to function properly when is accessed simultaneously by different users for different purposes. It needs to be capable to carry out the job for the users.
If the system encounters problems DBMS needs to be prompt and offer recovery solutions for the user.
The biggest issue of our times is Security. Of course that the DBMS must have powerful security structures. It’s a must to perform correctly password allocation. The DBMS needs to know which user has access to a Database and which his rights are. If a Database can be accessed by everyone then the data can be compromised.

Chapter IV

What is meant by program-data independence in the context of a database management system?

The advantages of program-data independence are that the DBMS manages with the metadata stored in it, so all other applications don’t need to worry about the data formats. Also queries and updates are managed by the DBMS and for that programs are not needed to process data access routines.
With program-data independence Databases are developed quicker and the maintenance process is much more productive than usual.

Chapter V

Explain by means of an example:
a) What is meant by data redundancy in a flat file
information and retrieval system?
b) How data in such a system might become inconsistent?

a) A DB stored on a flat file can cause eternal problemsJ.Data redundancy means that data is duplicated in many different files. Different systems or programs have separate copies of the same data. Just imagine how difficult will be to update data from such a system. You need to do that for each data stored from those different flat files even if is the same data in each flat file. This can cause real maintenance headaches, and it also compromises data integrity. Also it’s a waste of space to have duplicate items.
b) Data can become inconsistent in a flat file when data is changed. Just typing the same data so many times in different records can cause problems, and data become inconsistent. It can occur typing mistakes.

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