Transcript Notes of Chapter 8

Chapter 8
Managing Data Resources
Managing Data Resources
• 8.1 Organizing Data in a Traditional File
Environment
– An effective information system provides users with
timely, accurate, and relevant information.
– When the files are properly arranged and maintained,
users can easily access and retrieve the information.
– Well-managed, carefully arranged files make it easy to
obtain data for business decisions.
– 8.1.1 File Organization Terms and Concepts:
• A computer system organizes data in a hierarchy that starts
with bits and bytes and progresses to fields, records, files, and
databases.
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• A group of bits, called byte, represents a single
character, which can be letter, a number, or another
symbol.
• A grouping of characters into a word, a group of
words, or a complete number, is called field.
• A group of fields comprises a record.
• A group of records of the same type is called a file.
• A record describes an entity. An entity is a person,
place, thing, or event on which we maintain info.
• Each characteristic or quality describing a particular
entity is called an attribute.
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• Every record in a file should contain at least one field that
uniquely identifies that record, which is called key field.
– 8.1.2 Accessing Records from Computer Files
• Sequential file organization, data records must be retrieved in
the same physical sequence in which they are stored
• Direct/random file organization allows users to access
records in any sequence they desire.
• Transform algorithm is a mathematical formula to translate
the key field directly into the record’s physical storage location
on disk.
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– 8.1.3 Problems with the Traditional File
Environment
• Each functional area tended to develop systems in
isolation from other functional areas.
• The isolated systems lead to hundreds of programs
and applications.
• These systems result in data redundancy, programdata dependence, inflexibility, poor data security,
and inability to share data among applications.
• Data redundancy and confusion is the presence of
duplicate data in multiple data files.
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• Program-data dependence is the tight relationship between
data stored in files and the specific programs required to
update and maintain those files.
• Lack of flexibility means the inability to deliver ad hoc reports
or respond to unanticipated information requirements in a
timely fashion.
• Poor security for the data because of little control or
management of data, access to and dissemination of
information are virtually out of control.
• Lack of data-sharing and availability means it is hard for
people to obtain information as a result of the scattered pieces
of data among different files and different parts of the org.
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• 8.2 The Database Environment
– Database is a collection of data organized to serve
many applications efficiently by centralizing the data
and minimizing redundant data.
– 8.2.1 Database Management Systems
• It is simply the software that permits an organization to
centralize data, manage them efficiently, and provide access to
the stored data by application programs.
• It acts as an interface between application programs and the
physical data files.
• Three elements of database management system:
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• Data definition language is the formal language used by
programmers to specify the content and structure of the
database.
• Data manipulation language is the language used with other
conventional third- or fourth-generation lang. to manipulate the
data in the database and extract the needed data from it.
• Structured Query Language (SQL) is the most prominent
data manipulation lang.
• Data dictionary is an automated or manual tool for storing
and organizing information about the data maintained in a
database.
• Data element represents a field.
• Logical view presents data from end user’s perspective.
• Physical view shows how data are actually organized
physically.
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• 8.3 Designing Databases
– 8.3.1 Hierarchical Data Model
• The hierarchical data model presents data to users in a
treelike structure. Within each record, data elements are
organized into pieces of records called segments.
• Behind the logical view of data are a number of pointers,
which physically link the data items one to another.
– 8.3.2 Network Data Model
• The network data model is a variation of the hierarchical data
model.
• The databases can be translated from hierarchical to network
and vice versa to optimize processing speed and convenience.
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• Whereas the hierarchical depict one-to-many relationships,
network model depicts as many-to-many relationships.
• Each parent can have multiple children, and a child can have
more than one parent.
– 8.3.3 Relational Data Model
• The relational data model represents all data in the database
as simple two-dimensional tables called relations.
• Often a user needs information from a number of relations to
produce a report.
• It can relate data in any one file or table to data in another file
or table as long as both tables share a common data element.
• Three basic operations are used to develop useful sets of data:
select, project, and join.
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• Select creates a subset consisting of all records that meet a
condition criteria.
• Join operation combines tables to provide the user with more
information than is available in one table.
• Project operation creates a subset consisting of columns in a
table.
– 8.3.4 Advantages and Disadvantages of the Three
Database Models
• The advantage of network and hierarchical is processing
efficiency.
• Their disadvantage is that all the access paths, directories, and
indices must be specified in advance.
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• Moreover, they are both programming intensive and
time consuming, difficult to install, and difficult to
remedy.
• The strengths of relational DBMS are:
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great flexibility in regard to ad hoc queries,
power to combine info from different sources,
simplicity of design and maintenance, and
ability to add new data and records.
• However, these systems are somewhat slower
because they typically require many accesses to the
data stored on disk.
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– 8.3.5 Creating a Database
• Two design phases are required: conceptual and physical
designs.
• The physical design shows how the database is actually
arranged on direct access storage devices.
• Conceptual design describes how the data elements in the
database are to be grouped.
• It identifies the relationships among data elements and the
most efficient way of grouping data elements together to meet
information requirements.
• Entity-relationship diagram is a methodology for
documenting databases illustrating the relationship between
various entities in the database.
• Normalization is to create the small stable data structures.
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• 8.4 Database Trends
– 8.4.1 Distributed Databases
• A distributed database is one that is stored in more than one
physical location.
• Parts of the database are stored physically in one location, and
other parts are stored and maintained in other locations.
• Two main ways of distributing a database.
• The central database can be partitioned so that each remote
processor has the necessary data to serve its local area.
• Another strategy is to replicate the central database at all
remote locations.
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• Both distributed processing and distributed databases have
benefits and drawbacks.
• Distributed systems reduce the vulnerability of a single,
massive central site, permit increases in systems’ power by
purchasing smaller, less expensive computers, and increase
service and responsiveness to local users.
• However, they are dependent on high-quality
telecommunications lines, they can sometimes depart from
central data standards and definitions, pose security problems,
and the economies of distribution can be lost when remote site
buy more computing power.
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– 8.4.2 Object-Oriented and Hypermedia Databases
• The new applications require databases that can store and
retrieve drawings, photographs, voice, and full-motion video.
• Object-oriented database stores data and procedures as
objects that can be automatically retrieved and shared.
• The hypermedia database approach transcends some of the
limitations of traditional database by storing chunks of info in
the form of nodes connected by links established by the user.
• The relationship between records is less structured.
– 8.4.3 Multidimensional Data Analysis
• Some data analysis cannot be represented by traditional ways.
• Multidimensional analysis enables users to view the same data
in different ways using multiple dimensions.
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– 8.4.4 Data Warehouses
• Data warehouse is to integrate key operational data from
around the company in a form that is consistent, reliable, and
easily available for reporting.
• It is a database, with tools, that stores current and historical
data of potential interest to managers throughout the company.
• The data are available but cannot be altered.
• It includes a range of ad hoc and standardized query tools,
analytical tools, and graphical reporting facilities.
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• 8.5 Management Requirements for Database
Systems
– Much more is required for the development of database
systems than simply selecting a logical database model.
– 8.5.1 Data Administration
• Database systems require that the organization recognize the
strategic role of information and begin actively to manage and
plan for information as a corporate resource.
• Data admin is responsible for the specific policies and
procedures through which data can be managed as an
organizational resource (developing info policy, planning for
data, overseeing logical database design and data dictionary
development, and monitoring the data usage).
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• An organization needs to formulate an information policy that
specifies its rules for sharing, disseminating, acquiring,
standardizing, classifying, and inventorying information
throughout the org.
– 8.5.2 Data Planning and Modeling Methodology
• The org. requires enterprise-wide planning for data.
• The purpose of enterprise analysis is to identify the key
identities, attributes, and relationships that constitute the org.
data.
– 8.5.3 Database Technology, Management, and Users
• Databases require new software, new trained staff, and new
management structures.
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•
1.
2.
3.
4.
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The IS division is responsible for the technical and
operational aspects of managing data., which
called database admin that do the following:
Defines and organizes database structure and
content
Develops security procedures
Develops database documentation
Maintains the database mgmt software
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