Source Format Action Interface Book/Encyclopedia/Hand Written Search Literate. Paper tape coded use mechanist DB digital Search computer

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1 3. Data Bases (DB). DB is a collection of related files consisting of records that contains data, or collection of inter-related data stored together without redundancy to serve one or more applications in an optimal fashion. The data are stored so that they are independent of programs which use the data. The source of data can be internal or external; Table (3.1) shows some of the common sources and their characteristics. Source Format Action Interface Book/Encyclopedia/Hand Written Search Literate book and use user Journal Written Digest and apply specialist Drawing graphic Read and Trained use user Prototype geometric Measure and use Skilled user Paper tape coded use mechanist DB digital Search computer and use Disk digital use computer Table (3.1) Manufacturing data sources and their characteristics DB requirements

2 Seven reasons why companies need DB(s) are:- i. Redundancy. ii. Inconsistency. iii. The data can be shared. iv. Standards can be enforced. v. Security restrictions can be applied. vi. Integrity can be marinated. vii. Conflicting requirements can be balanced. Proper design of DB is critical to the usefulness of DB, since it affects how easily users can retrieve and use stored information. A long search indicates that the DB has not been designed carefully. DB design involves the followings:- # Accessibility: Information should be easy to find. # Administration: Information should be organized so the DB can evolve smoothly. Standards, procedures, and guidelines are followed for an effective administration. # Independency: information should not depend on the type and format of the reports being prepared. Once information has been located, report generation should be straight forward. #Integrity: Consistency, quality, and unambiguity of information are important. Since user's knowledge of DB may be limited, unintentional attempts at contamination are likely. A DB should have a safeguard against such attempts to ensure integrity and reliability of data.

3 #Interfacing: Being dynamic entities, data change with time. A welldesigned DB is easier to interface with past and future expansion. # Cost: The cost of developing and maintaining DB should be kept as low as possible. #Migration: Data should be stored that more commonly used data can be accessed quickly and conveniently. # Performance: DB performance is measured by its effectiveness in achieving intended objectives. # Redundancy: Information should not be stored at more than one location. This saves space and reduces search duration. # Reliability: information should be stored in a format so that reports and forms can easily use it. The DB involves two ongoing jobs: creation and updating, and use. To ensure the reliability of data only authorized personnel should be allowed to create and update it. The creator may be user, too but a user needs not to be the creator or updater. #Response time: The response to query and the throughputs should match or exceed the user dialogue rate. #Search flexibility. The user should be able to ask a verity of questions about the data stored.even unanticipated types of quarries may have to be entertained, requiring faster search. #Security: For security of classified and privileged information, access to unauthorized users must be denied. #Versatility: To provide users different logical files to work with, these files must be drivable from the same DB. Logical files are designed for user convenience and may bear little resemblance to how data is stored physically.

4 3.2. Basics of data arrangements and access. A computer system organize data in a hierarchy that begins with bit, and proceeds to byte, fields, records, files and DBs as shown in Fig (3.1) below. Bit: The smallest unit of data computer can process. Byte: Represent the most basic logical data element (character), which consists of a single alphabetic, numeric, or other symbol. Field: A grouping of characters, such as the grouping of alphabetic characters in someone name. A data field represents an attribute (a characteristic or quality) of some entity (object, person, place, etc.). Record: Related files of data are grouped to form a record. The record represents a collection of attributes that describes an entity. File:A group of related records is a data file or table. File Record Record Field Field Byte Field Byte Byte

5 Bit Bit Byte bit bit bit Fig(3.1)hierarchy of computer based data file Types of data models. The description of data and its relationships may be logical or physical. Logical description specifies the data type and associated relationships. A physical description refers to how data physically recorded on the hardware. A physical record may contain several logical records to save storage space and access time. There are three different data models are: Hierarchical, Networked, and Relational models as shown in the fig.(3.2) A:Hierarchical a: Hierarchical Automobile Body Engine Electronics Fuel Systems

6 B: Networked C: Relational Model Advantages Disadvantages. Hierarchical Searching is fast and efficient. Access to data is predefined by exclusively hierarchical relationships.

7 Networked Relational Many more relationships can be defined. There is great or speed and efficiency than with The RDB models. Conceptual simplicity: there are no predefined relationships among data. High flexibility in ad-hoc querying. New data and records can be added easily. Predetermined by administrator. Limited search/query flexibility. Not all data are Naturally hierarchical. This is the most complicated model to design, implementation, and maintain Grater query flexibility than with the hierarchical model less than with the R-model. Processing efficiency and speed are lower. Data redundancy is common, requiring additional maintenance. Advantages and Disadvantages of the Logical Data models in the DBs are shown in Table (3.2) Types of DBs. i. Operational DB. These DBs store detailed data needed to support the operations of the entire organization, they are also called Subject Area databases (SADB), transaction DBs, and production DBs, inventory DBs and other DBs generated by business operator. ii. Analytical DB. These DBs store data and information extracted from selected operational and external DBs. They consist summarized data and information most needed by an organization's managers and other end

8 users. Analytical DBs are also called management DBs or information DBs They may also be called multidimensional DBs, since they frequently use multidimensional database structure to organize data. These are the DBs accessed by online analytical processing (OLAP), decision support systems, and executive information systems. iii. Data warehouses. A data warehouse stores data from current and previous years that has been extracted from various operational and management DBs of an organization. It is the central source of data that has been screened, edited, standardized and integrated so it can be used by managers and other end user professionals throughout an organization. iv. Distributed DB. Have a complete copies or portion of the DB, in more than one location, which is usually close to the user. It is a DB that is under the control of a central database management system, in which storage devices are not all attached to common CPUs. It may be stored in multiple computers located in same physical location, or may be dispersed over a network of interconnected computers. Collections of data (in a DB) can be distributed across multiple physical locations. A distributed DB can reside on network servers on the Internet, on corporate intranets or extranets, or on other company networks. To ensure that the distributive DBs are up to date and current, there are two processes: replication and duplication (both of these processes can keep the data current in all distributive locations). Single site failure does not affect performance of system. v. End user DB.

9 This type of DB contains a verity of data files developed by en user at their workstations. vi. External DB. Access to a wealth of information from external DBs is available from a commercial online services, especially the www provides variety of hyperlinked pages of multimedia documents in the hypermedia DBs for the user to access 3.5. DB system Architecture. A generalized DB architecture may support 3 types of schemas (maps) as shown in fig (3.2) below; but not all the systems support all aspects. Schemas selected depending upon many factors such as; kind, type of data to be processed, No. of users, and Physical hardware available. Schemas are; the logical description of the entire database, and the listing of all data items, and their relationships. Types of schemas (is the model, plan, or structure around which fields, records and fields are organized). Each type is different view of DB, and each schema has different function Internal schemas: It is the low level representation (Physical computer hardware representation) that specifies how data physically are stored and accessed, how data files are represented, in what sequence? In what indexes exists External Schemas:-Describes how applications or users would see the data, so it is users oriented. It represents the data in most useful manner for particular application.

10 Conceptual Schemas. Define the logical structure of the DB. It is more abstract representation of data and it is halfway between the two above schemas. All access within the DB is handled through the Data Base Management System (DBMS). Fig (2.1) shows the generalized DB architecture. Fig.(3.3)A generalized DB architecture. Output Input Application Program External Schema DBMS Conceptual Schema Internal Schema Storage data level

11 3.6. DB Administrator (DBA). An information specialist who has the responsibility that falls in 4 areas are: DB planning: Involves working with mangers to find firm s schema and with the users to define their subschemas. DBA plays a key role in selecting DBMS DB Implementation: Consists of creating the DB to conform to the specifications selected of the DBMS, as well as establishing and enforcing policies for DB use DB Operation Includes offering educational programs to DB users and providing assistance when needed DB security: Includes the monitoring of DB activities using statistics provided by the DBMS. In addition, DBA ensures that the DB remains secure. Large firms have multiple DB specialists, who are managed by DBA (manager). 4. DB Users. The people who use the DB by entering the data and retrieving the information are called users. There are three broad classes of DB users are:- i. The application programmer who is responsible for writing application program that uses the DB. ii.end-user who access the DB from terminal usually by applications generated by application programmer. The end user may also employ query language provided as an integral part of the system. iii.dba.

12 There are also a number of other people working in DB development, as software support personnel and those who are with the operation of the hardware. Data model: a data model describes the approach or the rules used to structure a DB in a computer system. Examples as relational, hierarchical, etc. 5. Languages used in DBs. Different languages may be used in DBs as: i. Data Definition Language (DDL):It is used to describe the schema, the DB definitions, and the logical links between the data to the Data Base Management System(DBMS).It may be part of the DBMS ii. Data manipulation langue (DML):It is another DBs sublanguage, this language is used to describe only access or retrieval transactions and to pass data to user programs. iii. Host language: A host language is the ordinary programming language, such COBOL, FORTRAN, which is extended to permit DB transactions to be coded. 5. Performance measurements of DBs: Two performance measurements are:- i. Throughput: The number of tasks that can be completed in a given time interval. ii. Response time: The amount of time it takes to complete a single task from the time it is submitted. 6. Disadvantages of DBs.

13 The main disadvantage of DBs is their relative costs. They can be expensive to install, run, and maintain. However the alternative of having disorganized data may be more costly. DBs need large memories to store the DBMS, tables, directories, application programs, and so one. The implementation of DBS can be a major task requiring a great deal of preparatory planning and preparation. Staff require training, data must be loaded, application programs debugged, and so on. Thus the implementation of a DB can be significant cost in both cash terms and in terms of the time that company personnel need to invest in this implementation.

Managing Data Resources

Chapter 7 Managing Data Resources 7.1 2006 by Prentice Hall OBJECTIVES Describe basic file organization concepts and the problems of managing data resources in a traditional file environment Describe how