Introduction

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 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)?

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?

3. Network 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.

5. 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

6. 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?

7. System Concepts For 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.

8. 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.

10. 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.

11. System Concepts For Network Modeling • Business Geography • Example locations include:

12. 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

13. 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.

14. 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

15. 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.

17. 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.

19. 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.

20. 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.

21. 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.

23. 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?

24. 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-CRUDmatrix. • 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.

26. 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 system’s process response to various business and temporal events. • Both models should be synchronized.

27. 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.

28. 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.

30. 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

31. 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.

32. 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.

33. 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.

34. 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.

35. 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.

37. 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.

40. 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.

41. 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