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Client :a single-user computer that provides user interface services and appropriate

database and processing services, and connectivity services to servers (and possibly

other clients). Your World Wide Web brower is a client of a World Wide Web server.It runs client network access software which is called the requester or redirector

(e.g. Win 95).

Server : a multiple-user computer that provides shared database, processing, and

interface services, and connectivity to clients and other servers. It will have a

NOS(Network Operating System) that provide services such as file and print sharingand user account management(e.g. Win NT).

Client/server computing: an information system database, software, and interfaces

are distributed across a network of clients and servers that communicate and

cooperate to achieve system objectives. (Distributed computing, cooperativecomputing.)

Peer-to Peer: This has no servers and the network is used to share resources amongindependent peers. Every computer is both a client and a server

Client-Server Protocol: A communication protocol between networked computers in

which the services of one computer (the server) are requested by the other (the client).

Centralized computing: a multi-user computer hosts all the information system

components including the data storage, the business logic, and any system interfaces.

The user may interact with this host computer via a terminal, but all the work is doneon the host computer.

Network: A system of connected computers exchanging information with each other.Can be a LAN or WAN

Local area network (orLAN): a set of client computers through cable over

relatively short distances.

Wide area network ( orWAN): an interconnected set of LANs or the connection of

PC over a longer distance

There are two types of servers.

File-and-print servers:File Serversprovides services that allow network users to share files e.g. Windows NT.These services include things like file transfer, file storage and data migration, file update

synchronization (ensuring that each user has the latest version) and file archiving.

E.g.Stores the database, but the client computers must execute all database instruction.Such asAccess and dBASE.

Print Servers manage and control printing on a network, allowing multiple and

simultaneous access to printing facilities. The network operating system achieves this by


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using print queues, which are special storage areas where print jobs are stored and then

sent to the printer in an organized fashion.

Application(Database) servers: store the database, but the database commands are alsoexecuted on those servers. The clients merely send their database commands to the

server. The server returns only the result of the database command processing and notentire databases or tables. Such as oracle and SQL Server

Message servers: Not only files are passed between users. Data can take form ofgraphics, video, audio, text, binary e.g. Electronic mail, workgroup application(e.g.

workflow management applications and linked-object documents ), OO applications,

Directory services

Protocols : the agreed upon ways that computers exchange information

- Hardware protocol defines how hardware devices operate and work together(e.g.

10baseT Ethernet protocol)

Software protocol programs communicate with each other via this e.g. network

protocols:

- TCP/IP: Transmission Control Protocol/Internet Protocol - this protocol is thefoundation of the Internet, an agreed upon set of rules directing computers on how

to exchange information with each other. Other Internet protocols, such as FTP,

GopherandHTTP sit on top of TCP/IP. Good for large networks that use routers,networks connected directly to the Internet.

-

- IPX/SXP : Used in Novell Netware (NWLINK is Microsofts version). Good forlarge routed networks

- NETBIEU (IBM): NETBIOS(Network Basic Input/Output System) Extended

User Interface(used for small single server LAN networks)

- NFS : Unix uses Network File System to share file storage over a TCP/IP network

Bandwidth: A measurement of the volume of information that can be transmitted over a

network at a given time. Think of a network as a water pipe - the higher the bandwidth

(the larger the diameter of the pipe), the more data (water) can pass over the network

(through the pipe).

CGI: Common Gateway Interface - the specification for how an HTTP server shouldcommunicate with server gateway applications.

Cookies: Sweet snacks. Also the collective name for files stored on your hard drive by

your Web browser that hold information about your browsing habits, like what sites youhave visited, which newsgroups you have read, etc. Many view 'cookies' as an invasion of

privacy. To learn about ways to protect your privacy, visit this site for software and

information.
http://www.squareonetech.com/glossary.shtml#FTPhttp://www.squareonetech.com/glossary.shtml#FTPhttp://www.squareonetech.com/glossary.shtml#FTPhttp://www.squareonetech.com/glossary.shtml#GOPHERhttp://www.squareonetech.com/glossary.shtml#HTTPhttp://www.squareonetech.com/glossary.shtml#HTTPhttp://www.wizvax.net/kevinmca/http://www.squareonetech.com/glossary.shtml#FTPhttp://www.squareonetech.com/glossary.shtml#GOPHERhttp://www.squareonetech.com/glossary.shtml#HTTPhttp://www.wizvax.net/kevinmca/


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Domain: The Internet is divided into smaller sets known as domains, including .com

(business), .gov (government), .edu (educational), .mil(military) and others.

Domain Name: Allows you to reference Internet sites without knowing the truenumerical address.

FTP: File Transfer Protocol - a set of rules for exchanging files between computers via

the Internet.

Gateway: Computer hardware and software that allow users to connect from one

network to another.

GIF: Graphics Interchange Format - a common image format. Most images seen on web

pages are GIF files.

Host: The name of a specific machine within a largerdomain.

HTML: HyperText Markup Language - a collection of tags typically used in the

development of Web pages.

HTTP: HyperText Transfer Protocol - a set of instructions for communication between a

server and a World Wide Web client.

IRC: Internet Relay Chat - the system allowing Internet users to conduct online text

based communication with one or more other users. Eg. MSN Messenger

ISP: Internet Service Provider - the company which provides you with a connection to

the Internet via either a Dial-up Connectionor a Direct Connection. (e.g. ISDN)

IP Address: Internet Protocol Address - every computer on the Internet has a unique

identifying number, like 191.1.24.2.

Internet : Exchange data and information using standard language and protocols. Thispermits computers of all types and sizes all over the world to communicate. All the

computers connected to Internet are potential clients with access to a world of servers

Intranet : a secure network, usually corporate, that uses Internet technology to integrate

desktop, work group, and enterprise computing into a single cohesive framework

Network topology: describes how a network provides connectivity between the

computers on that network. All network topologies operate according to established

network protocols that permit different types of computers to communicate andinteroperate. SNA, TCP/IP.
http://www.squareonetech.com/#DOMAINhttp://www.squareonetech.com/#DIAL-UPhttp://www.squareonetech.com/#DIAL-UPhttp://www.squareonetech.com/#DIRECThttp://www.squareonetech.com/#DOMAINhttp://www.squareonetech.com/#DIAL-UPhttp://www.squareonetech.com/#DIRECT


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Nameserver: A computer running a program that converts domain names into

appropriate IP addresses and vice versa

Packet: A chunk of data. The TCP/IP protocol breaks large data files into smaller"packets" for transmission. When the data reaches its destination, the protocol makes sure

that all packets have arrived without error.

Page: An HTML document, or Web site.

PING: Ping - a program for determining if another computer is presently connected to

the Internet.

PGP: Pretty Good Privacy - an encryption scheme which uses the "public key" approach

- messages are encrypted using the publicly available key, but can only be deciphered by

the intended recipient via the private key.

URL: Uniform Resource Locator - the method by which Internet sites are addressed. Anexample would be "http://www.squareone.com", the address of the this home page.

Data architectures for distributed relational databases

Client/server computing helps on distributing data without loss of centralized

control. This control is being accomplished through distributed relational

databases.

Relational database: Data are stores as table format. Each file is implemented as

a table. Each field is a column in the table. Each record in the file is a row in the

table. Related records between two tables are implemented by intentionallyduplicating columns in the two tables.

Distributed relational database: distributes or duplicates tables to multiple

database servers. The program required to implement distributed relational

databases is called a distributed relational database management system.

Distributed relational database management system: is a software programthat controls access to and maintenance of the stored data. It also provides for

backup, recovery, and security. It is sometimes called a client/server database

management system.

Database engine: is that part of the DBMS that execute database commands tocreate, read, update, and delete records in the tables.

Most RDBMSs support two types of distributed data.


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Data distribution:partitions data to one or more database servers. Entire tables

can be allocated to different servers, or subsets of rows in a table can be

duplicated to different servers.

Data replication : duplicates data on one or more database servers. Entire tables

can be duplicated on different servers, or subsets of rows in a table can beduplicated to different servers.

Data architecture must specify the RDBMS and the degree to which data will bedistributed or replicated. An application data architecture is selected based on the

desired client/server model and the database technology needed to support that

model.

Relational Database Concepts (http://bus.tsud.edu/cis3330/protected/glossary.htm)

DDL - data definition language is used to define the database.

DML - database modeling language is used to manipulate the database and retrieve

records.

Logical data modeling is a business perspective of a project's data that is

independent of how it will be stored in the database. It describes the business datarequirements in a format where business users can understand it.

Physical data modeling is a data model that directly represents the logical data as it

will be stored in the DBMS. The physical model is derived from the logical model.

The methods for migrating from a logical to a physical model are as follows: The

entities become database tables and the attributes become database columns. Datatypes and field lengths are defined for each attribute.

- Indexes are created and system-enforced referential integrity rules are defined.

- Data definition language (DDL) is created to define the database and associatedtables.

- The tables are populated with domain values, which are the pre-defined values for

particular attributes (e.g., colors or models).

Application Data Model: the data model for a single system or application.

Online Transaction Processing (OLTP) : typically uses Entity-Relation (ER) DataModeling

Online Analytical Processing (OLAP). : typically uses a combination ofdimensional modeling and ER Data modeling.


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Data flow diagram(DFD) is one of very famous tool that pictures the flow of data

through a system and the work or processing performed by that system.It is also

called bubble chart, transformation graph, and process model

Entity :

- Object that represents an object in the real world that has one specific objective.It contains properties(fields/columns) that describes the entity. It also has

relationships with other entities which is expressed in a ER(Entity Relationship)

Diagram.- Each record has a Primary key - An attribute or group of attributes that uniquely

identifies a record within a table

- Secondary key A key that is used strictly for data retrieval purposes- Cardinality : defines the minimum and maximum number of occurrences of one

entity for a single occurrence of the related entity. Because all relationships are bi-

directional, cardinality must be defined in both directions for every relationship- Domain Integrity all the values an attribute can legitimately take on

- Entity integrity - The absence of null values in a primary key. Guarantees that

each entity will have a unique identity. One of two integrity rules for databases.

- Independent entity: one that exists regardless of the existence of any otherentity. Its primary key contains no attributes that would make it dependent on the

existence of another entity.

- Something about which you want to store data; typically a person, place, thing,concept, or event. Also called a record in the old file based system. Entities are

grouped together to form tables or entity sets.

Entity relationship diagram - A diagram that depicts an entity relationship modelsentities, attributes, and relations. It also displays connectivity and cardinality. The

entity relationship diagram is created during the design of the database. It might

also be used as a communications tool to help people understand the makeup of thedatabase.

Schema - A drawing of a relational database in which each table is represented by a

rectangle and the relationships between tables are represented by lines that connectthe rectangles. The table name appears at the top of the rectangle, with all attributes

listed inside and the primary key is usually in bold print. The lines start at the side of

the rectangle next to the place of the attribute used in the relationship. The type of

relationship is indicated by the symbols used next to the rectangles (1:M, 1:1, andM:M)

Existence dependent - A property of an entity whose existence depends on one or

more other entities. Represented by a double-square box in the E-R diagram.

Composite entity An entity that stands for the relationship between 2 or more otherentities. The most common use of composite entities in a relational database is to


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provide a way to express a many-to-many relationship as 2 one-to-many

relationships.

Normalization

Normalization - A process for assigning attributes to entities using principles thatwill greatly reduce or eliminate data redundancies.

Functional dependence - Within a relation R, an attribute B is functionally

dependent on an attribute A if and only if a given value of the attribute A determines

exactly one value of the attribute B. The relationship "B is dependent on A" isequivalent to "A determines B". In a properly designed table, if A is the primary key

of a table, all the attributes in the table should be functionally dependent on A.

Partial dependency - An attribute in a table is dependent on a portion of the primary

key, rather than the entire key. This situation is eliminated when the table is in second

normal form

Normal forms - Stages in the normalization process. There are seven normal forms,

however, most business databases are designed using only the first three normal

forms. See also 1NF, 2NF, and 3NF.

First normal form 1NF - First or lowest or the database design forms that require:

- all the key attributes are defined- there are no repeating groups

- all attributes are dependent on the primary key.

Second normal form 2NF - Second of the database design forms that require that thedata is in 1NF, and the data includes no partial dependencies, that is, no attribute is

dependent on only a portion of the primary key.

Third normal form 3NF Third of the database design forms that requires that the

data is in 2NF, and the data includes no transitive dependencies(An attribute in a table

is dependent on another non primary key attribute rather than the primary key. Thissituation is eliminated when the table is in third normal form)
http://bus.tsud.edu/cis3330/protected/glossary.htm#1NFhttp://bus.tsud.edu/cis3330/protected/glossary.htm#2NFhttp://bus.tsud.edu/cis3330/protected/glossary.htm#3NFhttp://bus.tsud.edu/cis3330/protected/glossary.htm#1NFhttp://bus.tsud.edu/cis3330/protected/glossary.htm#2NFhttp://bus.tsud.edu/cis3330/protected/glossary.htm#3NF


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Figure 4-10. Normalization example - denormalized data model.

The first step is to take the model to the first normal form (1NF). In the first normal form,

each attribute or column occurs only once for each instance of the primary key. Since acitizen can own multiple vehicles, the vehicle data moves to a new entity called Vehicle.

(See Figure 4-11.) This way, the data for each citizen is stored only once and multiple

vehicles owned by a citizen can exist without citizen data repeated. Characteristics of first

normal form are as follows:


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Figure 4-11. Normalization example - First Normal Form (1NF).

The next step is to take the model to second normal form (2NF). Second normal form

starts with the first normal form model, then any partial dependencies are removed so all

the non-key attributes are fully dependent on the composite primary key. In the example,the insurance company is not dependent on the composite primary key, so it is put into a

separate entity. (See Figure 4-12.) By definition, a model is already in second normal

form if it only has a single attribute primary key.


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Figure 4-12. Normalization example - Second Normal Form (2NF).

The final step is to take the model to third normal form (3NF). Third normal form startswith the second normal form model and then modifies it so that no attributes depend on

any other non-key attributes. As well, there are no attributes calculated from other

attributes. In third normal form, all attributes are dependent on the primary key and onlythe primary key. In the example, the county seat is dependent on the county, so a separate

county entity is added. (See Figure 4-13.)


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Figure 4-13. Normalization example - Third Normal Form (3NF).

Once a model has reached third normal form, any variation from that form is calleddenormalization. Queries against an ER model typically require the joining of two or

more tables together. The more joins required for a query, the more chance of

performance degradation. Denormalization is sometimes necessary in a data model toincrease the performance of data access.

Unary relationship - A relationship that exists within a single table. Example: A

table of employees might have as its primary key EMP-NUM. That same table

might have a field for the employee's manager which would contain the EMP-NUMof the manager of that employee. See also recursive relationship.

Recursive relationship A relationship that is expressed about multiple records withinone table. Example: A recursive relationship might be expressed within a universitys

class table if one course is a prerequisite of another course. See

Hierarchical database model (e.g. IMS)

A database model based on an upside-down tree structure in which each record is

called a segment. The top record is the root segment. Each segment has a 1:M


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relationship to the segment directly below it. (The basic data model of a hierarchical

model is a hierarchy or tree relationship where each segment of the tree has one

parent and can have many children).

A recursive hierarchical relationship is where the entity is both the parent and the

child and the relationship is non-identifying. An example of a recursive relationship iswhere a product can be constructed of multiple products stored in the same table.

Segment - A record in a hierarchical database model - part of a parent childrelationship. Each segment (except the root segment) has one parent segment and

may have one or more child segments.

Child A segment located below another segment in a hierarchical tree; each lower

segment is a child of the directly connected segment above it. (A child pointer is one

that points to a record that is one level down from the current record. A twin pointer

points to a record that shares the same parent as the current record and resides at the

same level as the current record)

Parent - The segment located above another segment in a hierarchical tree; eachsegment is a parent of the segments below it. See also child

Root - The first or top segment in a hierarchical database model.

Disadvantages of the hierarchical model include:

1. the designer of a hierarchical database must be concerned with physical storage

considerations

2. the designer of a hierarchical database must be conscious of the manner in whichdata are accessed

3. hierarchical databases do not permit user-friendly ad hoc queries

4. the hierarchical model cannot directly model m:m relationships

5. there is no standard

6. programming is difficult

Advantages of the hierarchical model

it is optimized for 1:m relationships stable, mature technology it handles sequential records processing efficiently

Hierarchical path - The ordered sequence of segments that must be accessed by the

hierarchical DBMS in order to retrieve a given segment
http://bus.tsud.edu/cis3330/protected/glossary.htm#Childhttp://bus.tsud.edu/cis3330/protected/glossary.htm#Child


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This child/parent rule assures that data is systematically accessible. To get to a low-level table,you start at the root and work your way down through the tree until you reach your target. Ofcourse, as you might imagine, one problem with this system is that the user must know how thetree is structured in order to find anything!

However, as you can imagine, the hierarchical database model has some serious problems. Forone, you cannot add a record to a child table until it has already been incorporated into the parenttable. This might be troublesome if, for example, you wanted to add a student who had not yetsigned up for any courses.

Worse, yet, the hierarchical database model still creates repetition of data within the

database. You might imagine that in the database system shown above, there may be ahigher level that includes multiple course. In this case, there could be redundancy becausestudents would be enrolled in several courses and thus each "course tree" would haveredundant student information. Redundancy would occur because hierarchical databaseshandle one-to-many relationships well but do not handle many-to-many relationships well.This is because a child may only have one parent. However, in many cases you will want tohave the child be related to more than one parent. For instance, the relationship betweenstudent and class is a "many-to-many". Not only can a student take many subjects but asubject may also be taken by many students. How would you model this relationship simplyand efficiently using a hierarchical database?


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Network database model (e.g. IDMS)

A database model that expresses a collection of records in M:M relationships known

as owner/member relationships. Each owner may own multiple members, andmultiple owners may own each member.

Owner - The record on the one side of a one to many relationship expressed in anetwork database model. The relationship is owner - member.

Faced with these serious problems, the computer brains of the world got together and came upwith the network model.

In many ways, the Network Database model was designed to solve some of the moreserious problems with the Hierarchical Database Model. Specifically, the Network model

solves the problem of data redundancy by representing relationships in terms of sets

rather than hierarchy.

The network model is very similar to the hierarchical model actually. In fact, the

hierarchical model is a subset of the network model. However, instead of using a single-

parent tree hierarchy, the network model uses set theory to provide a tree-like hierarchywith the exception that child tables were allowed to have more than one parent. This

allowed the network model to support many-to-many relationships

Visually, a Network Database looks like a hierarchcal Database in that you can see it as a type oftree. However, in the case of a Network Database, the look is more like several trees which sharebranches. Thus, children can have multiple parents and parents can have multiple children.

The network model was far from perfect. Most profoundly, the model was difficult toimplement and maintain. Most implementations of the network model were used by computerprogrammers rather than real users. Enter the Relational Database Model


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Advantages of the network model

1. Records more flexible and independent, can be accessed directly

2. Records have multiple access paths3. Records of the same type can be linked together with a loop

4. Physical pointers are the method of establishing relationships

Disadvantages of the network model

1. High skill level required to implement and maintain2. Update and delete very complex

Recursive Network Relationship

Network modeling:

Technique used to document the geographic structure of a system. It is also called

distribution modeling and geographic modeling.

Logical network models depict the perspective of the system owners and system users oninformation systems geography. Synchronization of data, process and interface building

blocks with those of the network models is needed.

Distributed computing, which allocates specific information system elements to

different computers that cooperate and inter-operate across a computer network, drives

the network modeling.

The distributed computers are:

Desktop and laptop computers

Shared network computers, clients

Legacy mainframe computers and minicomputers


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Network modeling: diagrammatic technique used to document the shape of a business or

information system in terms of its business locations.

Figure 7.1 shows an example of incomplete location activity diagram.

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