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flat file application vs database environment

answer

computer involves two components: data and instructions conceptually, there are two methods for designing the interface between program instructions and data: 1. file-oriented processing: a specific data file was created for each application (instructions first, data later) 2. data-oriented processing: create a single data repository to support numerous applications (data first, instructions later)

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flat-file problems

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types of issues: data storage data updating currency of information task-data dependency

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data storage (flat file problem)

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creates excessive storage costs of paper documents and/or magnetic form.

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data updating (flat file problem)

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any changes or additions must be performed multiple times

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currency of information (flat file problem)

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has the potential problem of failing to update all affected files

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task-data dependency (flat file problem)

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user unable to obtain additional information as his or her needs change

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flat-file problem solved

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types of issues: no data redundancy single update current values task-data independence

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no data redundancy (flat-file problem solved)

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except for primary keys, data is only stored once

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task-data independence (flat-file problem solved)

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users have access to the full domain of data available to the firm

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result of data redundancy

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files and data elements used in more than one application must be duplicated and because of this the characteristics of data elements and their values are likely to be inconsistent

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inaccessibility of data

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outputs usually consist of pre-programmed reports instead of ad-hoc queries provided upon request

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inflexibility of program

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changes to current file-oriented appliactions cannot be made easily nor can new developments be quickly realized

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database

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set of computer files that minimizes data redundancy and is accessed by one or more application programs for data processing the set of record types that an organization needs to support its business process

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database management system

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a computer program that enables users to create, modify, and utilize database information efficiently purpose is to provide controlled access to the database. DBMS is designed to know who has access to what.

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association

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the nature of the functional connection between two entities in a relation. is represented in an ER diagram by a verb label on the connecting line such as ships, requests, receives, and so on

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cardinality

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is the degree of association between two entities. simply stated, describes the number of possible occurences in one table that is associated with a single occurrence in a related table four basic forms zero or one(o:1), one and only one (1:1), zero or many (0:M) and one or many (1:M)

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disadvantages of database approach

answer

-can be costly to implement(hard/soft ware, storage, and network resources) -can only run in certain operating environments (may be unsuitable for some system configurations) -because so different from file approach, requires training users (can be resist to change)

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elements of the database environment

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1. users 2. applications (unsure) 3. DBMS (database management system) 4. DBA (database administrator) 5. physical database

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users

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individuals who employ systems, receive information, and act on the information received access the database in two ways 1. application programs-request information from DBMS 2. via direct query- retrieving data in a friendly manner to provide an ad hoc management report

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applications

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requests information from the DBMS, which in turns validates the requests and retrieves the data for processing.

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DBMS feature

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program development- backup and recovery- database usage reporting- database access-

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program development

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user created applications

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backup and recovery

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copies database

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database usage reporting

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captures statistics on database usage(who, when , etc.)

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database access

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authorizes access to sections of the database

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user programs

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makes the presence of teh dbms transparent to the user

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direct query

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allows authorized users to access data without programming

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database administrator (DBA)

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responsible for managing the database resource. having multiple users share a common database requires organization, coordination, rules, and guidelines to protect the integrity of the database.

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responsibilities of the DBA

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-database planning(coding schemes) -design (tables and relationship forms and queries) -implementation- (create database in access create procedure manual) -operation and maintenance -change and growth

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database planning (responsibilities of the DBA)

answer

develop organizations database strategy define database environment define data requirements develop data dictionary

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design (responsibilities of the DBA)

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logical database(schema) external users' view (subschemas) internal view of database database controls

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implementation (responsibilities of the DBA)

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determine access policy implement security controls specify test procedures establish programming standards

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operation and maintenance (responsibilities of the DBA)

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evaluate database performance reorganize database as user needs demand review standards and procedures

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change and growth (responsibilities of the DBA)

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plan for change and growth evaluate new technology

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database conceptual models (3)

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hierarchical model network model relational model

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relational model

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-portrays data in the form of two dimensional 'tables' -its strength is the ease with which tables may be linked to one another -based on the relational algebra functions of restrict, project, and join -linked- PK from one table and embed as attribute in another table in its then referred to a foreign key

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data attribute/ field

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a single item of data

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entity

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database representation of an individual resource, event, or agent about which we choose to collect data

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record type

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table or file

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difference in association and cardinality

answer

association- represented by a line connecting two entities described by a verb, such as ships, requests, or receives cardinality- the degree of association between two entities the number of possible occurences in one table that are associated with a single occurrence in a related table used to determine primary keys and foreign keys

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s system is relational if:

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1. represents data in the form of two-dimensional tables 2. supports the relational algebra functions of restrict, project, and join restrict-row project- attribute(column) join- two tables consisting of all concatenated pair of rows

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three types of anomalies

answer

insertion deletion update

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insertion anomaly

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a new item cannot be added to the table until at least one entity uses a particular attribute item so you add a vendor but have not purchased inventory yet, the table provided will not add the vendor until you buy something, thus an insertion error

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deletion anomaly

answer

if an attribute item used by only one entity is deleted, all information about that attribute item is lost so we dont need part num 1 anymore and we delete it from the records, then vendor 27 will be delete cause thats the only item they sell to us, even though we want to keep them on file, the information is lost

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update anomaly

answer

a modification on an attribute must be made in each of the rows in which the attribute appears is the result of data redundancy in an unnormalized table an inventory table list 3 different parts and list the same vendors address in each of those rows, so everytime address is updated, its an update of informatoin 3 times, think big with 10,000 vendors

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normalization process

answer

systematically splits unnormalized complex tables into smaller tables that meet two conditions: 1. all nonkey(secondary) attributes in the table are dependent on the primary key 2. all nonkey attributes are independent of the other nonkey attributes when unnormalized tables are split and reduced to third normal form, they must then be linked together by foreign keys.

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six phases in designing relational databases

answer

1. identifying entities 2. construct a data model showing entity associations 3. add primary keys and attributes(are descriptors) exact columns you need 4. normalize and add foreign keys 5. construct the physical database 6. prepare the user views

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identifying entities (six phases in designing relational databases)

answer

identify the primary entities(resources, agents, events, misc.-rf) of the organization - what is table about? construct a data model- entity relation diagrams of their relationships

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construct a data model showing entity associations (six phases in designing relational databases)

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determine the association between entities

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add primary keys and attributes (six phases in designing relational databases)

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assign primary keys to all entities in the model to uniquely identify records every attribute should appear in one or more user views-(form, query ar report(doc), dont store data that you will never use)

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normalize and add foreign keys (six phases in designing relational databases)

answer

remove repeating groups, partial and transitive dependencies assign foreign keys to be able to link tables

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construct the physical database (six phases in designing relational databases)

answer

create physical tables populate tables with data

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prepare the user views (six phases in designing relational databases)

answer

normalized tables should support all required views of system users user view restrict users from having access to unauthorized data

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access controls audit procedures: verify

answer

responsibility for authority tables and subschemas granting appropriate access authority use or feasibility of biometric controls use of encryption

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database backup

answer

automatic periodic copy of data

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transaction log

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list of transactions that provides an audit trail

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checkpoint features

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suspends data during system reconciliation

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recovery module

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restarts the system after a failure

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backup controls (audit procedure:verify)

answer

that production databases are copied at regular intervals backup copies of the database are stored off site to support disaster recovery

Ch. 9 Database Management Systems – Flashcards

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