Copyright Irwin/McGraw-Hill 1998 1 Network Modeling Prepared by Kevin C. Dittman for Systems...

Prepared by Kevin C. Dittman for

Systems Analysis & Design Methods 4ed

by J. L. Whitten & L. D. BentleyCopyright Irwin/McGraw-Hill 19981

Network Modeling

Introduction

The chapter will address the following questions: Why may network modeling become an important skill for

applications developers in the next several years? What is the description network modeling and explain why it is

important? What is the definition of a system in terms of locations, location

types, and clusters? How can you factor a system’s or application’s locations into

component locations using a special location decomposition diagram?

How can you document the connections and essential data flows between locations using location connectivity diagrams (LCDs)?




Network Modeling

Introduction

The chapter will address the following questions: What is the complementary relationship between network,

process, and data models? How can you synchronize data, process, interface, and network

models to provide a complete and consistent logical system specification?

How is network modeling useful in different types of projects and phases?




Network ModelingNetwork Modeling - Not Just For Computer

Networks

Computer Networks Have become the nervous system of today’s information systems. The computer network is a physical component of an information

system. Must be created to support the logical distribution of data,

processes, and interfaces of an information system. Network modeling is a technique for documenting the

geographic structure of a system. Synonyms include distribution modeling and geographic modeling.




Network ModelingINFORMATION SYSTEMS FRAMEWORK

SYSTEM

ANALYSTS

SYSTEMBUILDERS

(components)

SYSTEMDESIGNERS

(specification)

SYSTEMUSERS

(requirements)

SYSTEMOWNERS

(scope)

DatabaseTechnology

(and standards)

Data Requirements

Logical Data Model

FOCUS ONSYSTEM

DATA

Business Processes

Logical Process Model

FOCUS ONSYSTEM

PROCESSES

Interface Requirements

Logical Interface Model

FOCUS ON SYSTEM

INTERFACES

Software(and Hardware)

Technology

(and standards)

InterfaceTechnology

(and standards)

NetworkingTelchnology

(and standards)

Communication Reqts.

Location ConnectivityDiagram

Operating Locations

Location Decomposition

FOCUS ONSYSTEM

GEOGRAPHY

Definition Phase

(establish and

prioritize

business system

requirements)

Study Phase

(etablish system

improvemetn

objectives)

Survey Phase

(establish scope &

project plan)

FASTMethodology

EDI Cust

St. Louis

HQ

LA Office

Indy Ware- house

NY Office

West Customers

East Customers

Maintenance Records

Products Catalog

ordercatalog

changes

ship order

ship order ship order

credit credit

service




Network ModelingNetwork Modeling - Not Just For Computer

Networks

Computer Networks The need for network modeling is being driven by a technical

trend – distributed computing. Distributed computing is the assignment of specific

information system elements to different computers which cooperate and interoperate across computer network. A synonym is client/server computing; however, client/server is actually one style of distributed computing.

The distributed computers include:• desktop and laptop computers, sometimes called clients

• shared network computers, called servers

• legacy mainframe computers and minicomputers




Network Modeling

System Concepts For Network Modeling

Today’s systems analyst must seek answers to new questions:

What locations are applicable to this information system or application?

How many users are at each location? Do any users travel while using (or potentially using) the system? Are any of our suppliers, customers, contractors, or other external

agents to be considered locations for using the system? What are the user’s data and processing requirements at each

location? How much of a location’s data must be available to other

locations? What data is unique to a location?




Network Modeling


Today’s systems analyst must seek answers to new questions: (continued)

How might data and processes be distributed between locations? How might data and processes be distributed within a location?

A network modeling tool is needed to document what we learn about a business system’s geography and requirements.

Network modeling is a diagrammatic technique used to document the shape of a business or information system in terms of its business locations.




Network Modeling


Business Geography Logical network modeling is the modeling of business network

requirements independent of their implementation. All information systems have geography. The location connectivity diagram (LCD) models system

geography independent of any possible implementation. A location connectivity diagram (LCD) is a logical network

modeling tool that depicts the shape of a system in terms of its user, process, data, and interface locations and the necessary interconnections between those locations.




Network Modeling

Suppliers (275)

Buyers (20)

on-the-road

Accounts Payable Office

(Atlanta)

Central Warehouse

(Atlanta)

Inventory Control Manager's Office

(Atlanta)

Purchasing Clerks

(3) Atlanta

Distribution Center

(New York)

Distribution Center

(Chicago)

Distribution Center

(Los Angeles)




Network Modeling


Business Geography The location connectivity diagram (LCD) illustrates two concepts

– locations and connectivity. The concept of geography is based on locations.

• A location is any place at which users exist to use or interact with the information system or application. It is also any place where business can be transacted or work performed.

Business management and users will tend to identify logical locations where people do work or business.

Information technologists will tend to discuss physical locations where computer and networking technology is located.

Location




Network Modeling


Business Geography Example locations include:

Logical locations – places where data arecollected, work is performed, orinformation is needed

Implementation Locations – placeswhere computers, peripherals, and otherinformation technology is located

City Computer centerCampus Network serverBuilding PC or terminal locationOffice Local area networkWork area (e.g., warehouse) Wide area network hub/gatewaySubsidiaryHome officeCustomer, supplier, or contractor




Network Modeling


Business Geography Logical locations can be:

scattered throughout the business for any given information system.

on the move (e.g., traveling sales representatives). external to the enterprise for which the system is being built.

For instance, customers can become users of an information system via the telephone or the Internet.

Logical locations can represent: clusters of similar locations organizations and agents outside of the company but which

interact with or use the information system; possibly (and increasingly) as direct users




Network Modeling


Business Geography Derivatives of the rectangle will be used to illustrate different

types of locations. The standard rectangle will be used to represent a specific

location. The rectangle with the double, vertical lines will be used to

represent a cluster of locations. Some locations are not stationary, a rounded rectangle will

represent their mobility. Some locations represent external organizations and agents

(such as customers, suppliers, taxpayers, contractors, and the like). A parallelogram to illustrate these external locations.

Specific Location

Moving or Mobile Location(s)

Cluster of "like"

locations

External Location




Network Modeling


Business Geography Location names should describe the location and/or its users. Examples of location names follows:

Paris, France Indianapolis, Indiana Grissom Hall Building 105 Grant Street building Room 222 Warehouse Rooms 230-250 Shipping Dock Order Clerk User names (as locations) Order Entry Dept. Customers Order clerks (a cluster) Suppliers Students




Network Modeling


Business Geography Some locations consist of other locations and clusters. It can be quite helpful to understand the relative decomposition of

locations and types of location. Decomposition is the act of breaking a system into its

component subsystems. Each ‘level’ of abstraction reveals more or less detail (as desired) about the overall system or a subset of that system.

In systems analysis, decomposition allows you to partition a system into logical subsets of locations for improved communication, analysis, and design. A location decomposition diagram shows the top down

geographic decomposition of the business locations to be included in a system.




Network Modeling

Inventory Control System

Geography

New York Distribution

Center

Chicago Distribution

Center

Atlanta Headquarters

Los Angeles Distribution

Center

Inventory Control

Manager

Purchasing Agents

(4)

Accounts Payable Office

Buyers (15-25)

Accounts Payable

Managers (2)

Accounts Payable Clerks

(3)




Network Modeling


Business Geography The purpose of network modeling is to help system designers

distribute the technical data, processes, and interfaces across the computer network.

The systems analyst needs to specify the technology-independent communications that must occur between business locations.

The communication between business locations requires connectivity. Connectivity defines the need for, and provides the means for

transporting essential data, voice, and images from one location to another.

Connections between locations represent the possibility of data flows between locations.




Network Modeling

New York Distribution

Center

Chicago Distribution

Center

Los Angeles Distribution

Center

Inventory Control

Manager

Purchasing Agents

(4)

Buyers (15-25)

Accounts Payable

Managers (2)

Accounts Payable Clerks

(3)

Suppliers




Network Modeling


Miscellaneous Constructs There are no universal standards for location connectivity

diagrams; therefore, in appropriate situations it is permissible to annotate LCDs with symbols from other models, such as data flow diagrams.




Network Modeling


Synchronizing of System Models Network, data, interface, and process models represent different

views of the same system, but these views are interrelated. Modelers need to synchronize the different views to ensure

consistency and completeness of the total system specification.




Network Modeling


Synchronizing of System Models Data and Process Model Synchronization:

There should be one data store in the process models for each entity in the data model. Also, there are sufficient processes in the process model to maintain the data in the data model.

The synchronization quality check is stated as follows: • Every entity should have at least one C, one R, one U, and one D

entry for system completeness. If not, one or more event processes were probably omitted from the process models. More importantly, users and management should validate that all possible creates, reads, updates, and deletes have been included.




Network Modeling

Entity . Attribute Pro

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Customer C C R R R R

.Customer Number C C R R R R

.Customer Name C C U R R R

.Customer Address C C U RU RU RU

.Customer Credit Rating C U R R R

.Customer Balance Due RU U R R

Order C D RU RU

.Order Number C R R

.Order Date C U U

.Order Amount C U U

Ordered Product C D CRUD CRUD RU

.Quantity Ordered C CRUD CRUD

.Ordered Item Unit Price C CRUD CRUD

Product R R R R C D RU RU RU

.Product Number R R R R C R

.Product Name R R R C RU

.Product Description R R R C RU

.Product Unit of Measure R R R C RU RU

.Product Current Unit Price R R R U

.Product Quantity on Hand RU U RU RU RU




Network Modeling


Synchronizing of System Models Data and Network Model Synchronization:

A data model describes the stored data requirements for a system as a whole.

The network model describes the business operating locations. The goal is to identify what data is at which locations. Specifically, the following business questions might be asked:

• Which subset of the entities and attributes are needed to perform the work to be performed at each location?

• What level of access is required?

• Can the location create, read, delete, or update instances of the entity?




Network Modeling


Synchronizing of System Models Data and Network Model Synchronization: (continued)

System analysts have found it useful to define logical requirements in the form of a Data-to-Location-CRUD matrix.

• A Data-to-Location-CRUD Matrix is a table in which the rows indicate entities (and possibly attributes); the columns indicate locations; and the cells (the intersection rows and columns) document level of access where C = create, R = read or use, U = update or modify, and D = delete or deactivate.




Network Modeling

Entity . Attribute Cu

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Customer INDV ALL ALL SS SS SS SS

.Customer Number R R CRUD R CRUD R CRUD R

.Customer Name RU R CRUD R CRUD R CRUD R

.Customer Address RU R CRUD R CRUD R CRUD R

.Customer Credit Rating X R RU R R

.Customer Balance Due R R RU R R

Order INDV ALL SS ALL SS SS SS SS

.Order Number SRD R CRUD R CRUD R CRUD R CRUD R

.Order Date SRD R CRUD R CRUD R CRUD R CRUD R

.Order Amount SRD R CRUD CRUD R CRUD R CRUD R

Ordered Product INDV ALL SS ALL SS SS SS SS

.Quantity Ordered SUD R CRUD R CRUD R CRUD CRUD

.Ordered Item Unit Price SUD R CRUD CRUD R CRUD CRUD

Product ALL ALL ALL ALL ALL ALL ALL ALL ALL

.Product Number R CRUD R R R R R R R

.Product Name R CRUD R R R R R R R

.Product Description R CRUD RU R R R R R R

.Product Unit of Measure R CRUD R R R R R R R

.Product Current Unit Price R CRUD R R R R R R

.Product Quantity on Hand X RU R R RU R RU

INDV = individual ALL = ALL SS = subset X = no access

S = submit C = create R = read U = update D = delete




Network Modeling


Synchronizing of System Models Process and Interface Model Synchronization:

The The context diagram was previously introduced as an interface model that documents how the system you are developing interfaces to business, other systems, and other organizations.

DataData flow diagrams document the system’s process response to various business and temporal events.

BothBoth models should be synchronized.




Network Modeling


Synchronizing of System Models Process and Network Model Synchronization:

Process models illustrate the essential work to be performed by the system as a whole.

Network models identify the locations where work is to be performed.

Some work may be unique to one location. Other work may be performed at multiple locations.

Before designing the information system, what processes must be performed at which locations should be identified and documented.




Network Modeling


Synchronizing of System Models Process and Network Model Synchronization:

Synchronization of the process and network models can be accomplished through a Process-to-Location-Association Matrix.

• A Process-to-Location-Association Matrix is a table in which the rows indicate processes (event or elementary processes); the columns indicate locations, and the cells (the intersection rows and columns) document which processes must be performed at which locations.




Network Modeling

Process Cu

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Process Customer Application X X X X

Process Customer Credit Application X X

Process Customer Change of Address X X X X

Process Internal Customer Credit Chnage X

Process New Customer Order X X X X

Process Customer Order Cancellation X X X X

Process Customer Change to Outstanding Order X X X X

Process Internal Change to Customer Order X X X

Process New Product Addition X

Process Product Withdrawal from Market X

Process Product Price Chnage X

Process Product Chnage to Product Specification X X

Process Product Inventory Adjustment X X X




Network Modeling

The Process of Logical Network Modeling

Network Modeling during Strategic Systems Planning Projects

Many systems planning methodologies and techniques result in a network architecture to guide the design of all future computer networks and applications that use those networks. May be a traditional map, or a top-down decomposition

diagram that logically groups locations. Association matrices are also typically used to provide an

initial mapping of data entities to locations, and processes to locations




Network Modeling


Network Modeling during Systems Analysis During the study phase of systems analysis, a project team should

review any existing network models, logical or physical. In the definition phase of systems analysis, network modeling

becomes more important. If a network model already exists, it is expanded or refined to

reflect new application requirements. If a network model does not exist, a network model should be

built from scratch.




Network Modeling


Looking Ahead to Systems Design The logical application network model from systems analysis

describes business networking requirements, not technical solutions.

In systems design, network models must become more technical – they must become physical network models that will guide the technical distribution and duplication of the other physical system components, namely, DATA, PROCESSES, and INTERFACES.




Network Modeling


Fact-Finding and Information Gathering for Network Modeling

Like all system models, network models are dependent on appropriate facts and information as supplied by the user community.

Facts can be collected by sampling of existing forms and files; research of similar systems; surveys of users and management; and interviews of users and management.

The fastest method of collecting facts and information, and simultaneously constructing and verifying the process models is Joint Application Development (JAD). JAD uses a carefully facilitated group meeting to collect the

facts, build the models, and verify the models – usually in one or two full-day sessions.




Network Modeling


Computer-Aided Systems Engineering (CASE) for Network Modeling

Network models should be stored in the repository. Computer-aided systems engineering (CASE) technology provides

the repository for storing various models and their detailed descriptions.




Network Modeling

How to Construct Logical Network Models

Location Decomposition Diagram Decomposition diagrams are used to logically decompose and

group locations.

Building The Location Decomposition Diagram First, brainstorm your locations. Think of all of the places where

direct and indirect users of your system will be located. To group locations in the decomposition diagram, keep similar

locations on the same level or within the same branch of the tree. Clustering reduces clutter through simplification; however, there is

a danger of oversimplifying the model. Cluster a location or its users if the data and processing

requirements for all users are expected to be the same.




Network Modeling

Member ServicesSys. Geography

Indianapolis

MarketingOffice

AdvertisingOffice

Sales Office

Baltimore SeattleProspectiveMembers

Members

Warehouse

Order EntryClerks

SalesManagers

Sales Office Warehouse

Order EntryClerks

SalesManagers

Sales Office

Order EntryClerks

SalesManagers

Portland

Warehouse




Network Modeling

How to Construct Logical Network Models

Location Connectivity Diagram Location connectivity diagrams can be initially drawn at a high-

level to communicate general information. More detailed information can be added to subsequent diagrams.

In the following slides, the first location connectivity diagram drawn is a systemwide model. It will include any external locations and locations that have sublocations. The second diagram reveals an exploded view.




Network Modeling

Members

ProspectiveMembers

Seattle

Portland

Baltimore

Indianapolis

indeterminate distance

indeterminate distance

2250 miles

2250 miles

575 miles




Network Modeling

Balt. Order EntryClerks (8)

Indpls. Order EntryClerks (12)

Indpls. AdvertisingOffice (4)

Indpls. MarketingOffice (3)

Seattle SalesManagers (2)

Seattle Order EntryClerks (7)

Members (n)

Balt. SalesManagers (2)

Members (n)

Port. WarehouseStations (2)

Balt. WarehouseStations (3)

Indpls. WarehouseStations (3)

Indpls. SalesManagers (3)

Members (n)

ProspectiveMembers (n)

Figure 7.10

Indeterminate Distance


2250 miles

575 miles

250 feet

50 feet

< 150 feet

200 miles


< 40 feet

< 20 feet


< 50 feet

580 feet

2250 miles

2800 miles

575 miles




Network Modeling

The Next Generation

The Next Generation The demand for logical network modeling skills will remain

strong so long as the trend towards distributed computing remains strong.

CASE tool support will evolve after methodologies, since CASE tool engineers are reluctant to invest time and effort prior to some semblance of a widely accepted methodological standard.




Network Modeling

Summary

Introduction Network Modeling - Not Just For

Computer Networks

System Concepts For Network Modeling The Process of Logical Network Modeling How to Construct Logical Network Models The Next Generation

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