The chapter will address the following questions:

The chapter will address the following questions:
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)? 262 In this chapter you will learn how to use a unique network modeling tool, location connectivity diagrams, to document a business system’s logical network locations, independent of a physical computer system’s network. A logical network model will be used to determine how actual data and processes will be distributed to those locations.

The chapter will address the following questions:
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? 262 No additional notes provided.

Network Modeling - Not Just For 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. It is frequently argued that “the network is the computer.” The phenomenal growth of the Internet signals that this trend will continue.

265 Figure 7.1 Network Modeling Relationship with the IS Building Blocks Logical network models are used to document an information system’s GEOGRAPHY focus from the perspective of the system owners and system users (the intersection of the GEOGRAPHY column with the system owner and system user rows). The horizontal arrow suggests the need to synchronize the DATA, PROCESS, and INTERFACE building blocks with those of the network models, especially for the system user perspective.

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 266 The dominant desktop operating systems are Microsoft’s Windows, Windows 95, and Windows NT Workstation with smaller market shares for Apple’s System 7 and 8, and IBM’s OS/2. The server market includes Intel- and RISC-based processors that run network operating systems such as UNIX, Novell, and Windows/NT Server. With each passing day, these servers are encroaching on territory that was once the exclusive domain of minicomputers and mainframes. The mainframe (e.g., IBM System 370 series) and minicomputer (e.g., IBM AS/400 series) are not dead! But they are no longer the central focus in distributed computing. Instead, they might best be thought of as a superserver in a distributed computing network. The growth of physical networks has created a need to better understand the logical business networks to be supported by the technology. This need is further amplified by such business trends as: globalization of the economy the vision of an information superhighway increasing numbers of corporate mergers and acquisitions the growth of strategic partnerships with customers, suppliers, contractors, and even competitors

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? 266 Distributed computing technology is evolving faster than our ability to properly apply it. System designers need to make intelligent decisions about the distribution of data, processes, and interfaces when designing today’s applications. But how do the systems designers make those decisions? The answer is old and proven – “Develop business savvy. Talk to your management and users before you talk to the technical networking specialists!”

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. 267 Unlike process modeling (with data flow diagrams) and data modeling (with entity relationship diagrams), there are no generally accepted network modeling standards. Thus, we had to invent a tool, location connectivity diagrams (LCDs).

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. 267 Consistent with data and process modeling, logical models will eventually be followed by physical models that describe the system design of networks and the distributed solution.

267-268 Figure 7.2 Logical Network Model
The figure above illustrates a simple, and incomplete location activity diagram. The shapes indicate different types of locations and the connections indicate the need for business connectivity and interoperability between the locations.

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. 268 No additional notes provided.

Business Geography Example locations include: 268 No additional notes provided.

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 268 No additional notes provided.

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. Each location within the cluster is actually a simple location, but for the sake of simplicity, we represent “like” locations as a single location. One has to use some common sense judgment in deciding when to cluster locations. A group of locations or users should be represented as a single cluster if it is expected that they will likely share the same data and processes (to be assigned from the data and process models. Some locations are not stationary. Sales representatives and purchasing agents may be on the road, but nonetheless they use your information system. But they still be considered to be part of the system or application that you are 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 Shipping Dock Order Clerk User names (as locations) Order Entry Dept. Customers Order clerks (a cluster) Suppliers Students 269 Use proper nouns for locations, but use titles for users. Use singular and plural nouns where appropriate. Plural names are appropriate for clusters.

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. For example, a University may have many campuses and extension sites. A campus may include many buildings. A building may include many types of offices, classrooms, laboratories, and other dedicated space – and many instances of each type.

270 Figure 7.3 Location Decomposition Diagram
A location decomposition diagram is one view of system geography.

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. For example, a University may have many campuses and extension sites. A campus may include many buildings. A building may include many types of offices, classrooms, laboratories, and other dedicated space – and many instances of each type.

270-271 Figure 7.4 Location Connectivity Diagram
Connectivity requirements might be expressed as follows: For this application, the NEW YORK DISTRIBUTION CENTER (a cluster) needs to communicate with or interact with the PURCHASING AGENT OFFICES. The figure above illustrates this requirement as a location connectivity diagram (LCD). Connections are drawn without arrows because each connection is a conceptual two-way highway that may support numerous business data flows that must pass between locations. Also, until we know how data and processes will be distributed to locations (a system design decision) we can’t possibly know which business data flows will travel each connection or direction. As an LCD progresses from logical requirements to physical design, specific data flows will need to be associated with connections, and the volume of data traffic for each connection will have to be summed. Connections are not named on the LCD. It is useful, however, to label each connection by noting the distance between locations. A range of distances should be indicated for mobile locations.

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. 272 External agents symbols might be included to represent external connections that absolutely will not be directly connected to your system. Suppose we want to directly place orders for stock with our largest suppliers only. We’ll use mail for all other suppliers. This can be represented on our LCD with two symbols: an external location circle labeled DIRECT SUPPLIERS and a DFD external agent labeled INDIRECT SUPPLIERS. In this case both symbols should be drawn in the same general area. Another useful DFD symbol might be the data store. When used on an LCD it distributes or attaches specific data storage to that location.

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. 272 No additional notes provided.

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. 272 No additional notes provided.

272-273 Figure 7.5 Data-to-Process-CRUD Matrix
The decision to include or not include attributes is based on whether processes need to be restricted as to which attributes they can access.

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? No additional notes provided.

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. No additional notes provided.

273-274 Figure 7.6 Data-to-Location-CRUD Matrix
The decision to include or not include attributes is based on whether locations need to be restricted as to which attributes they can access.

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. 274 Purists argue that every business event’s trigger (a data or control flow) and the system response (additional data and control flows) should appear on the context diagram as well as in the data flow diagrams. Some methodologies and CASE tools strictly enforce this rule. Because most systems must respond to dozens of events, the net result of this purist approach is a very complex context diagram with large numbers of data flows to and from the single process. (Recall that a context diagram represents the entire system as a single process.) Pragmatists suggest that the above context diagram loses its communication value. We tend to agree and suggest that the context diagram illustrate the ‘big picture’ and only include the key data flows the illustrate the main purpose of the system. At the same time, we would argue that all of the data flows on the context diagram should be included or represented in the subsequent data flow diagrams. In other words, you can add additional events and responses in the DFDs, but you must include or represent the events and responses from the context diagram into the DFDs.

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. No additional notes provided.

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. 275 No additional notes provided.

275 Figure 7.7 Process-to-Location Association Matrix
Once validated for accuracy, the system designer will use this matrix to determine which processes should be implemented centrally or locally. Some methodologies and CASE tools may support views of the process model that are appropriate to a location. If so, these views (subsets of the process models) must be kept in synch with the master process models of the system as a whole.

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 276 No additional notes provided.

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. 276 It is probably not worthwhile to draw a network model for an existing system since the project vision may radically change the model.

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. 276 No additional notes provided.

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. 276 No additional notes provided.

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. 276 Curiously, although CASE tool vendors have embraced distributed computing solutions, they have been slow to provide computer-assisted, logical network modeling. There is, however, a workaround in most CASE tools. Most CASE tools provide some sort of open-ended modeling tool to support generic presentation graphics or system flowcharting. Such tools can be adapted for use as network models. Obviously, you may have to select different shapes for the different location symbols.

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. If the DFDs are already completed, study the external agents to identify possible external locations. Don’t forget to add moving or mobile locations to the list. Be creative in considering how your network my be extended to the outside world. To group locations in the decomposition diagram, keep similar locations on the same level or within the same branch of the tree. For example, don’t combine cities with buildings or buildings with rooms. Instead, keep cities with cities, buildings with buildings, and rooms with rooms. It makes the diagrams easier to read. More importantly, it makes it possible to produce a leveled set of LCDs (much in the manner that functional decomposition diagrams made it possible to produce a sensibly partitioned set of data flow diagrams). Cluster a location or its users if the data and processing requirements for all users are expected to be the same. For example, rather than show each ORDER ENTRY CLERK, it probably makes more sense to show one location labeled ORDER ENTRY CLERKS (plural). On the other hand, if these same clerks are in significantly different locations, or they are grouped into classifications that have different authorities or responsibilities, you might want to factor ORDER ENTRY CLERKS into more refined clusters.

277 Figure 7.8 SoundStage Location Decomposition Diagram
There is only one symbol used on the location decomposition diagram—the location—and it is the same location symbol used in LCDs. The locations are connected to form a top-down, treelike structure. A parent location may consist of those child locations beneath it.

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. 278 No additional notes provided.

278 Figure 7.9 High-Level SoundStage Location Connectivity Diagram
Notice that we included an external location called MEMBER. This external location was selected to fulfill a system goal to permit members to directly execute transactions and inquiries, just like SoundStage’s own staff. We might implement such a requirement as a touch-tone telephone response system, or an Internet World Wide Web or Gopher page for members with their own PCs). The implementation is not yet relevant, but the external location is. Notice that we also included sublocation symbols for each city. These can now be exploded to reveal the sublocations and their interactions. Finally, notice that each connection’s distance is recorded.

278-279 Figure 7.10 Detailed SoundStage Location Connectivity Diagram
Notice that the connections from the parent location were brought down from the system diagram. This maintains consistency between the diagrams. The new nodes correspond to the parent’s child nodes on the decomposition diagram. It’s all very straightforward. Once again the connections are labeled to reflect distances. This diagram could have contained additional sublocation nodes. If so, those nodes would have to be exploded to their own diagram. Once again, the parent’s connections would be carried down to the more detailed level to preserve balancing.

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. All viable methodologies will incorporate some type of logical network modeling paradigm to deal with distributed computing. A variation on data flow diagramming is the most likely candidate to emerge as a defacto standard. As important as the model itself, are the underlying descriptions of locations and connections. In the meantime, many CASE tools are providing the technology to grow your own network modeling tool by attaching custom-built descriptions and properties to shapes on a system flowchart or presentation tool.

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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