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  • 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. 265
  • 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 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!” 266
  • 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). 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
  • 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. 267-268
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  • 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 268-269
  • Use proper nouns for locations, but use titles for users. Use singular and plural nouns where appropriate. Plural names are appropriate for clusters. 269
  • 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. 269-270
  • Figure 7.3 Location Decomposition Diagram A location decomposition diagram is one view of system geography. 270
  • 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. 269-270
  • 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. 270-271
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  • 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. 272-273
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  • 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. 273-274
  • 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. 274
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  • 275 No additional notes provided.
  • 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. 275
  • 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. 277
  • 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
  • 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. 278-279

Transcript

  • 1.  
  • 2. 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
  • 3. 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?
  • 4. 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.
  • 5. System Concepts For Network Modeling
    • Business Geography
      • L ogical 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.
  • 6.  
  • 7. 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.
  • 8. System Concepts For Network Modeling
    • Business Geography
      • Example locations include:
  • 9. 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
  • 10. 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.
  • 11. 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
  • 12. 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.
  • 13.  
  • 14. 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.
  • 15.  
  • 16. 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.
  • 17.  
  • 18. 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?
  • 19. 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.
  • 20.  
  • 21. 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.
  • 22. 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.
  • 23. 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.
  • 24.  
  • 25.  
  • 26.  
  • 27.