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Chapter 14: Design Method --- data and architectural design Design -- A multistep process in which representations of data structure, program structure, interface characteristics, and procedural detail are synthesized.
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December 25, 1997 R. A. Volz -- Assistance - Haichen Liu, Brian Bolstad 2 Why Architecture? The architecture is not the operational software. Rather, it is a representation that enables a software engineer to: (1) analyze the effectiveness of the design in meeting its stated requirements, (2) consider architectural alternatives at a stage when making design changes is still relatively easy, and (3) reduce the risks associated with the construction of the software.
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December 25, 1997 R. A. Volz -- Assistance - Haichen Liu, Brian Bolstad 3 Why is Architecture Important? l Representations of software architecture are an enabler for communication between all parties (stakeholders) interested in the development of a computer-based system. l The architecture highlights early design decisions that will have a profound impact on all software engineering work that follows and, as important, on the ultimate success of the system as an operational entity. l Architecture “constitutes a relatively small, intellectually graspable model of how the system is structured and how its components work together” [BAS03].
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December 25, 1997 R. A. Volz -- Assistance - Haichen Liu, Brian Bolstad 4 Data Design l What is data design? n Transform the information domain model created during analysis into data structure required to implement the software n Well-designed data lead to better program structure and modularity, reduced procedural complexity
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December 25, 1997 R. A. Volz -- Assistance - Haichen Liu, Brian Bolstad 5 Data Design l At the architectural level … n Design of one or more databases to support the application architecture n Design of methods for ‘mining’ the content of multiple databases –navigate through existing databases in an attempt to extract appropriate business-level information –Design of a data warehouse—a large, independent database that has access to the data that are stored in databases that serve the set of applications required by a business
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December 25, 1997 R. A. Volz -- Assistance - Haichen Liu, Brian Bolstad 6 Data Design l At the component level … n refine data objects and develop a set of data abstractions n implement data object attributes as one or more data structures n review data structures to ensure that appropriate relationships have been established n simplify data structures as required
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December 25, 1997 R. A. Volz -- Assistance - Haichen Liu, Brian Bolstad 7 Data Design Process l Define data structures identified during the requirements and specification phase. n Often base decision on algorithm to be used. l Identify all program modules that must operate directly upon the data structure n Constrain the scope of effect of data design decisions l Or, from OO perspective, define all operations performed on the data structure
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December 25, 1997 R. A. Volz -- Assistance - Haichen Liu, Brian Bolstad 8 Principles of Data Design (Component Level) l A data dictionary should be established and used for both data and program design l Low-level data design decisions should be deferred until late in the design process l A library of useful data structures and the operations that may be applied to them should be developed. -- Reuse n E.g., stacks, lists, arrays, queues
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December 25, 1997 R. A. Volz -- Assistance - Haichen Liu, Brian Bolstad 9 Principles of Data Design (cont.) l The representation of data structures should be known only to those modules that must make direct use of the data contained within the structure. n Information hiding l The software design and programming languages should support the specification and realization of abstract data types.
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December 25, 1997 R. A. Volz -- Assistance - Haichen Liu, Brian Bolstad 10 Architectural Styles l Data-centered architectures l Data flow architectures l Call and return architectures l Object-oriented architectures l Layered architectures Each style describes a system category that encompasses: (1) a set of components (e.g., a database, computational modules) that perform a function required by a system, (2) a set of connectors that enable “communication, coordination and cooperation” among components, (3) constraints that define how components can be integrated to form the system, and (4) semantic models that enable a designer to understand the overall properties of a system by analyzing the known properties of its constituent parts.
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December 25, 1997 R. A. Volz -- Assistance - Haichen Liu, Brian Bolstad 11 Data-Centered Architecture
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December 25, 1997 R. A. Volz -- Assistance - Haichen Liu, Brian Bolstad 12 Data Flow Architecture
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December 25, 1997 R. A. Volz -- Assistance - Haichen Liu, Brian Bolstad 13 Call and Return Architecture
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December 25, 1997 R. A. Volz -- Assistance - Haichen Liu, Brian Bolstad 14 Layered Architecture
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December 25, 1997 R. A. Volz -- Assistance - Haichen Liu, Brian Bolstad 15 Architectural Design l Objective n develop a modular program structure and represent control relationships between modules l Data flow-oriented design (Structured design) n amenable to a broad range of applications n very useful when information is processed sequentially, such as microprocessor control application; complex, numerical analysis procedure; etc. n two approaches (transform and transaction mapping)
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December 25, 1997 R. A. Volz -- Assistance - Haichen Liu, Brian Bolstad 16 Structured Design l objective: to derive a program architecture that is partitioned l approach: n the DFD is mapped into a program architecture n the PSPEC and STD are used to indicate the content of each module l notation: structure chart
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December 25, 1997 R. A. Volz -- Assistance - Haichen Liu, Brian Bolstad 17 Architectural Design Process l Five-step Process n the type of information flow is established n flow boundary are indicated n data flow diagram is mapped into program structure n control hierarchy is defined by factoring n resultant structure is refined using design measures heuristics
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December 25, 1997 R. A. Volz -- Assistance - Haichen Liu, Brian Bolstad 18 Architectural Design Process (cont.) l Transform Flow A B transform center incoming flow outgoing flows C
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December 25, 1997 R. A. Volz -- Assistance - Haichen Liu, Brian Bolstad 19 Architectural Design Process (cont.) l Transaction Flow T Transaction center Transaction Action paths
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December 25, 1997 R. A. Volz -- Assistance - Haichen Liu, Brian Bolstad 20 Transform Mapping l Allow data flow diagram(DFD) with transform flow characteristics to be mapped into a predefined template for program structure
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December 25, 1997 R. A. Volz -- Assistance - Haichen Liu, Brian Bolstad 21 Level 0 Safehome DFD
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December 25, 1997 R. A. Volz -- Assistance - Haichen Liu, Brian Bolstad 22 Level 1 Safehome DFD
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December 25, 1997 R. A. Volz -- Assistance - Haichen Liu, Brian Bolstad 23 Level 2 Safehome DFD - Monitor
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December 25, 1997 R. A. Volz -- Assistance - Haichen Liu, Brian Bolstad 24 Transform Mapping (cont) l Design steps n Step 1. Review the fundamental system model. n Step 2. Review and refine data flow diagrams for the software. n Step 3. Determine whether DFD has transform or transaction flow characteristics. –in general---transform flow –special case---transaction flow
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December 25, 1997 R. A. Volz -- Assistance - Haichen Liu, Brian Bolstad 25 Level 3 DFD for Monitor Sensors
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December 25, 1997 R. A. Volz -- Assistance - Haichen Liu, Brian Bolstad 26 Transform Mapping (cont) l step 4. Isolate the transform center by specifying incoming and outgoing flow boundaries n different designers may select slightly differently n transform center can contain more than one bubble. l step 5. Perform “first-level factoring” n program structure represent a top-down distribution control. n factoring results in a program structure(top-level, middle-level, low-level) n number of modules limited to minimum.
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December 25, 1997 R. A. Volz -- Assistance - Haichen Liu, Brian Bolstad 27 First Level Factoring
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December 25, 1997 R. A. Volz -- Assistance - Haichen Liu, Brian Bolstad 28 Transform Mapping (cont) n step 6. Perform “second-level factoring” –mapping individual transforms(bubbles) to appropriate modules. –factoring accomplished by moving outwards from transform center boundary. n step 7. Refine the first iteration program structure using design heuristics for improved software quality.
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December 25, 1997 R. A. Volz -- Assistance - Haichen Liu, Brian Bolstad 29 Second Level Factoring
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December 25, 1997 R. A. Volz -- Assistance - Haichen Liu, Brian Bolstad 30 First-Cut Program Structure
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December 25, 1997 R. A. Volz -- Assistance - Haichen Liu, Brian Bolstad 31 Refined Program Structure
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December 25, 1997 R. A. Volz -- Assistance - Haichen Liu, Brian Bolstad 32 Transaction Mapping A single data item triggers one or more information flows
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December 25, 1997 R. A. Volz -- Assistance - Haichen Liu, Brian Bolstad 33 Transaction Mapping Design l Step 1.Review the fundamental system model. l Step 2.Review and refine DFD for the software l Step 3.Determine whether the DFD has transform or transaction flow characteristics l Step 4. Identify the transaction center and flow characteristics along each of the action paths –isolate incoming path and all action paths –each action path evaluated for its flow characteristic.
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December 25, 1997 R. A. Volz -- Assistance - Haichen Liu, Brian Bolstad 34 Transaction Mapping (cont) l step 5. Map the DFD in a program structure amenable to transaction processing n incoming branch –bubbles along this path map to modules n dispatch branch –dispatcher module controls all subordinate action modules –each action path mapped to corresponding structure
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December 25, 1997 R. A. Volz -- Assistance - Haichen Liu, Brian Bolstad 35 Transaction Mapping
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December 25, 1997 R. A. Volz -- Assistance - Haichen Liu, Brian Bolstad 36 First Level Factoring
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December 25, 1997 R. A. Volz -- Assistance - Haichen Liu, Brian Bolstad 37 First-cut Program Structure
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December 25, 1997 R. A. Volz -- Assistance - Haichen Liu, Brian Bolstad 38 Transaction Mapping (cont) l step 6. Factor and refine the transaction structure and the structure of each action path l step 7. Refine the first iteration program structure using design heuristics for improved software quality
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December 25, 1997 R. A. Volz -- Assistance - Haichen Liu, Brian Bolstad 39 Design Postprocessing l A processing narrative must be developed for each module l An interface description is provided for each module l Local and global data structures are defined l All design restrictions/limitations are noted l A design review is conducted l “Optimization” is considered (if required and justified)
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December 25, 1997 R. A. Volz -- Assistance - Haichen Liu, Brian Bolstad 40 Summary - Data & Architectural l Data design translates the data objects defined in the analysis model into data structure that reside with in the software l Architectural design use information flow characteristics described in the analysis model to derive program structure l DFD is mapped into program structure use two approaches: transform and transaction mapping
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