The chapter will address the following questions:

1
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 systems or applications
  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)?

2
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?

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Network Modeling - Not Just For Computer Networks

• Computer Networks
• Have become the nervous system of todays
  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.

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Network 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

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System Concepts For Network Modeling

• Todays 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 users data and processing
  requirements at each location?
• How much of a locations data must be available
  to other locations? What data is unique to a
  location?

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System Concepts For Network Modeling

• Todays 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 systems 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.

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System Concepts For 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.

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System Concepts For 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.

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System Concepts For Network Modeling

• Business Geography
• Example locations include

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System Concepts For 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

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System Concepts For 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.

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System Concepts For 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

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System Concepts For 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.

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System Concepts For 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.

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System Concepts For 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.

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System Concepts For 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.

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System Concepts For 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.

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System Concepts For 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?

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System Concepts For 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.

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System Concepts For Network Modeling

• Synchronizing of System Models
• Process and Interface Model Synchronization
• 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.
• Data flow diagrams document the systems process
  response to various business and temporal events.
  
• Both models should be synchronized.

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System Concepts For 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.

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System Concepts For 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.

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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

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The Process of Logical 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.

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The Process of Logical 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.

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The Process of Logical 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.

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The Process of Logical 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.

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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.

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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.

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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.

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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