Transcript Architecture Design

Architecture Design
Speaker: Kuan-Ta Lu
Date: March 31
Software Engineering Phases – The
Design Phase
• In the design phase the architecture(結構) is
established. This phase starts with the requirement
document delivered by the requirement phase and
maps the requirements into an architecture.
• The architecture defines the
– Components
– interfaces
– behaviors
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(1)Architecture
• The architecture defines the components(元件),
interfaces, and behaviors of the system.
• The components are composed with other
components using their interfaces.
• An interface forms a common boundary of two
components. The interface is the architectural
surface where independent components meet and
communicate with each other. Over the interface,
components interact and affect each other.
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(2)Implementation Plan
• The implementation plan establishes the schedule
and needed resources. It defines implementation
details including programming languages, platforms,
programming environments, debuggers, and many
more.
• The implementation(執行) plan could be considered
as part of the design, which is the position taken
here, or it could be considered as the first
accomplishment in the implementation phase.
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(3)Critical Priority Analysis
• The critical priority analysis generates a list of
critical tasks. It is absolutely necessary to
successfully accomplish a critical(關鍵) task. The
project will succeed or fail based on the outcome of
these tasks. Some projects may have more than one
critical task.
• There are two major categories of critical tasks.
– One category of tasks are associated with the building of
the system.
– The other category of critical tasks are associated with the
system itself.
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(4)Performance Analysis
• Once given the typical scenarios from the
requirement document, the system can be designed
to meet performance(效能) objectives(目標).
• Different system architectures will yield different
predicted(預測) performance characteristics(特徵)
for each typical scenario.
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(5)Test Plan
• The test plan defines the testing necessary to
establish quality for the system.
• Ideally, 100 percent test coverage of the entire
system would be nice, but this is seldom achieved.
Creating a test suite that covers 90 percent of the
entire system is usually simple. Getting the last 10
percent requires significant amount of development
time.
• Systems are full of undiscovered bugs. The customer
becomes a logical member of the testing team and
bug fixes are pushed off to the next release.
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Data Flow Diagrams (DFD)
• Data Flow Diagrams are used for functional modeling.
As the name suggests, it is a diagram depicting the
flow of data through the system.
• DFDs (also called data flow graphs) are commonly
used during problem analysis. DFDs are quite general
and are not limited to problem analysis for software
requirements specification(規範).
• DFDs are very useful in understanding a system and
can be effectively used during analysis.
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Data Flow Diagrams (DFD) (con.)
• The DFD aims to capture the transformations that
take place within a system to the input data so that
eventually the output data are produced.
• The agent that performs the transformation of data
from one state to another is called a process (or a
bubble). So a DFD shows the movement of data
through the different transformation or process in
the system.
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Data Flow Diagrams (DFD) (con.)
• DFDs are basically of 2 types:
– Physical DFDs are used in the analysis phase to study the
functioning of the current system.
– Logical DFDs are used in the design phase for depicting the
flow of data in proposed system.
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(1)Elements of Data Flow Diagrams
• Data Flow Diagrams are composed of the four
basic symbols shown below.
– The External Entity symbol represents sources of data
to the system or destinations of data from the system.
– The Data Flow symbol represents movement of data.
– The Data Store symbol represents data that is not
moving (delayed data at rest).
– The Process symbol represents an activity that
transforms or manipulates the data (combines,
reorders, converts, etc.).
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(1)Elements of Data Flow Diagrams
(con.)
• External Entities
– External entities determine the system boundary.
– They are external to the system being studied.
– They are often beyond the area of influence of the
developer.
– These can represent another system or subsystem.
– These go on margins/edges of data flow diagram.
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(1)Elements of Data Flow Diagrams
(con.)
• Data Flow
– Data flow represents the input (or output) of data to (or
from) a process ("data in motion").
– Data flows only data, not control.
– Represent the minimum essential data the process needs.
Using only the minimum essential data reduces the
dependence between processes
– Data flows must begin and/or end at a process.
– Data flows are always named. Name is not to include the
word "data".
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(1)Elements of Data Flow Diagrams
(con.)
• Data Stores
– Data Stores are repository for data that are temporarily or
permanently recorded within the system.
– It is an "inventory" of data.
– These are common link between data and process models.
Only processes may connect with data stores.
– Data stores are named with an appropriate name, not to
include the word "file”.
OR
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(1)Elements of Data Flow Diagrams
(con.)
• Processes
– Processes are work or actions performed on incoming data
flows to produce outgoing data flows.
– These show data transformation or change.
– Data coming into a process must be "worked on" or
transformed in some way. Thus, all processes must have
inputs and outputs.
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(2)An Example of a DFD for a System
That Pays Workers
DFD of a system that pays workers.
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(3)Conventions(常規) used when
drawing DFD's
• It should be pointed out that a DFD is not a flowchart. A
DFD represents that flow of data, while flow chart shows
the flow of control.
• A DFD does not represent procedural information.
• Following are some suggestion for constructing a data
flow graph
– Klork your way consistently from the inputs to the outputs, or
vice versa(反之亦然). If you get stuck(問題), reverse direction.
Start with a high level data flow graph with few major
transforms describing the entire(整個) transformation from the
inputs to outputs and then refine each transform with more
detailed transformation.
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(3)Conventions used when drawing
DFD's (con.)
– Never try to show control logic. If you find yourself
thinking in terms of loops and decisions, it is time to stop
and start again.
– Label each arrow with proper data elements. Inputs and
outputs of each transform should be carefully identified.
– Make use of * and + operation and show sufficient detail in
the data flow graph.
– Try drawing alternate data flow graphs before setting on
one.
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Structure Charts
• In modular programming, the complete system is
coded as small independent interacting modules.
Each module is aimed at doing one specific task.
• The design for these modules is prepared in the form
of structure charts.
• A structure chart is a design tool that pictorially(形象
地) shows the relation between processing modules
in computer software.
• Describes the hierarchy of components modules and
the data are transmitted between them.
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Structure Charts (con.)
Fig 6.2 - Notation used in structure charts.
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Structure Charts (con.)
Fig 6.3 – Annotations(註解) and data passing in structure charts
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Structure Charts (con.)
• Data passing
– When one module calls another, the calling module can
send data to the called module so that it can perform(執行)
the function described in its name.
– Two types of data are transmitted.
• The first, parameter data, are items of data needed in the called
module to perform the necessary work.
• In addition, control information (flag data) is also passed. Its
purpose is to assist(協助) in the control of processing by indicating
the occurrence(發生) of, say, errors or end-of-conditions.
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Data Modeling and Data
Requirements
• The data model focuses on what data should be
stored in the database while the function model
deals with how the data is processed.
Fig 7.1 - Elements of conceptual design
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Data Modeling and Data
Requirements (con.)
Fig 7.2 - Overall Database Design Process
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E-R Data Modeling Technique
• The ER model is a conceptual(概念上) data model
that views the real world as a construct of entities
and associations or relationships between entities.
• A basic component of the model is the EntityRelationship diagram, which is used to visually
represent data objects.
• The constructs used in ER model can easily be
transformed into relational tables.
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E-R Model concept
• Entities
– An entity is any distinguishable(可區別的) object about
which information is stored.
– Another classification of entities can be independent or
dependent (strong or weak) entity.
• An independent entity is one, which does not rely on another
entity for identification.
• A dependent entity is one that relies on another entity for
identification.
Fig 7.6 - Physical and Abstract Entity
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E-R Model concept (con.)
• Attributes
– Attributes are basically properties of entity. We can use
attributes for identifying and expressing entities.
Fig 7.7 - Entity and its attributes
Fig 7.8 - Employee entity and its attribute values
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Types of Attributes
• Key or non-key Attributes
– Identifiers(標籤), more commonly called keys or key
attributes uniquely identify an instance(實例) of an entity.
– A descriptor(敘述) describes a non-unique characteristic of
an entity instance.
– An entity usually has an attribute whose values are distinct
for each individual entity.
– There may be a case when one single attribute is not
sufficient to identify entities. Then a combination of
attributes can solve this purpose.
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Types of Attributes (con.)
• Required or optional Attributes
– When it's required, we must have a value for it, a value
must be known for each entity occurrence.
– When it‘s optional(可選擇的), we could have a value for it,
a value may be known for each entity occurrence.
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Types of Attributes (con.)
• Simple and composite Attributes
– Composite(組合) attributes can be divided into smaller
subparts. These subparts represent basic attributes with
independent meanings of their own.
– Attributes that can’t be divided into subparts are called
Simple or Atomic attributes.
Composite Attributes
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Types of Attributes (con.)
• Single-valued and multi-valued Attributes
– Attributes that can have single value at a particular
instance of time are called single-valued.
– A multi-valued attribute can have more than one value at
one time.
• Stored, coded, or derived Attributes
– The attribute from which another attribute value is derived
is called stored attribute.
– Derived attributes are usually created by a formula or by a
summary operation on other attributes.
– A coded value uses one or more letters or numbers to
represent a fact.
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Entity Types
• An entity set is a set of entities of the same type that
share the same properties, or attributes.
• Entity sets don’t need to be disjointed.
Fig. 7.10 Two entity types and some of the member entities of each
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Designing basic model and E-R
Diagrams
• In order to begin constructing the basic model, the
modeler must analyze the information gathered
during the requirement analysis for the purpose of:
and
– classifying data objects as either entities or attributes,
– identifying and defining relationships between entities,
– naming and defining identified entities, attributes, and
relationships,
– documenting this information in the data document.
– Finally draw its ER diagram.
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Designing basic model and E-R
Diagrams (con.)
• E-R diagrams constructs
ENTITY TYPE
WEAK ENTITY TYPE
RELATIONSHIP TYPE
ATTRIBUTE
KEY ATTRIBUTE
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Designing basic model and E-R
Diagrams (con.)
MULTIVALUED ATTRIBUTE
DERIVED ATTRIBUTE
TOTAL PARTICIPATION OF E2 IN R
Cardinality Ratio 1:N FOR E1:E2 IN R
Structural Constraint(Min,Max) On
Participation Of E In R
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Designing basic model and E-R
Diagrams (con.)
Fig. 7.13 E-R Diagram of Library Management System.
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The End~
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