Download - Requirements Analysis
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Chapter 8Analysis Modeling
Adapted by Dan Fleck from:- Roger Pressman’s Slides- http://www.informatics.sussex.ac.uk/users/lb203/se/SE04.pdf- Jochen Rick’s slides from GA Institute of Technology- http://webfuse.cqu.edu.au/Courses/aut2001/95169/
Extra_Examples/DFD_Example_1/- System Analysis and Design slides edited by Yale Braunstein
Coming up: Requirements Analysis
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Requirements Analysis Requirements analysis
specifies software’s operational characteristics indicates software's interface with other system elements establishes constraints that software must meet
Requirements analysis allows the software engineer (called an analyst or modeler in this role) to: elaborate on basic requirements established during earlier
requirement engineering tasks build models that depict user scenarios, functional activities,
problem classes and their relationships, system and class behavior, and the flow of data as it is transformed.
Coming up: Analysis Phase: What is it?
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Analysis Phase: What is it?
systemdescription
analysismodel
designmodel
Three objectives:
• To describe what the customer requires
• To establish a basis for the creation of a software design
• To define a set of requirements that can be validated once the software is built
Three objectives:
• To describe what the customer requires
• To establish a basis for the creation of a software design
• To define a set of requirements that can be validated once the software is built
Coming up: Analysis Modeling Approaches
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Analysis Modeling Approaches
Structural analysis: The data: The model defines their attributes and
relationships. The processes that transform the data: The
model shows how they transform the data objects as they flow through the system.
Object-oriented analysis: Focus: Classes and their inter-relationships UML is predominantly object-oriented
But don’t be to dogmatic!Coming up: Elements of the Analysis Model
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Elements of the Analysis Model
Use-case diagrams
Use cases - text
Activity Diagrams
Swim lane diagrams
Scenario-based elements
Class diagrams
Analysis Packages
CRC Models
Collaboration Diagrams
Class-based elements
Data-flow diagrams
Control flow diagrams
Processing narratives
Flow-oriented elements
State diagrams
Sequence diagrams
Behavioral elements
Analysis Model
Coming up: Elements of the Analysis Model
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Elements of the Analysis ModelScenario-based elements
Class-based elements
Flow-oriented elements
Behavioral elements
Coming up: Class-Based Modeling
High level idea of the system from user’s or a functional perspective
How information flows throughout the system (data and control flow)
How the system responds to external stimuli
Static view of the system and how the different parts are related. Tries to show standard ideas of object oriented development
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Class-Based Modeling Identify analysis classes by examining
the problem statement Use a “grammatical parse” to isolate
potential classes Identify the attributes of each class Identify operations that manipulate the
attributes
Coming up: Grammatical Parsing
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Grammatical Parsing
Write an informal description of the problem. The
customer requirements document is one such
description.
Underline all nouns in the description
Decide which of these are really objects which the
project requires and organize them in related
clusters
Coming up: Grammatical Parsing
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Grammatical ParsingUniversity Bank will be opening in Oxford, Mississippi, in January,
2000. We plan to use a full service automated teller machine (ATM)
system.The ATM system will interact with the customer through a
display screen, numeric and special input keys, a bankcard reader, a
deposit slot, and a receipt printer.Customers may make deposits,
withdrawals, and balance inquires using the ATM machine, but the
update to accounts will be handled through an interface to the
Accounts system.Customers will be assigned a Personal Identification
Number (PIN) and clearance level by the Security system. The PIN can
be verified prior to any transaction.In the future, we would also like to
support routine operations such as a change of address or phone
number using the ATM
Coming up: Grammatical Parsing
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Grammatical Parsing University Bank will be opening in Oxford, Mississippi, in
January, 2000. We plan to use a full service automated teller machine (ATM) system.The ATM system will interact with the customer through a display screen, numeric and special input keys, a bankcard reader, a deposit slot, and a receipt printer.Customers may make deposits, withdrawals, and balance inquires using the ATM machine, but the update to accounts will be handled through an interface to the Accounts system.Customers will be assigned a Personal Identification Number (PIN) and clearance level by the Security system. The PIN can be verified prior to any transaction.In the future, we would also like to support routine operations such as a change of address or phone number using the ATM
Coming up: Typical Classes (a reminder)
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Typical Classes (a reminder) External entities - printer, user, sensor Things - reports, displays, signals Occurrences or events (e.g., interrupt, alarm) Roles (e.g., manager, engineer, salesperson) Organizational units (e.g., division, team) Places (e.g., manufacturing floor or loading dock) Structures (e.g., sensors, four-wheeled vehicles, or computers)
But, how do we select classes?
Coming up: Selecting Classes—Criteria
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Selecting Classes—Criteria
needed services – needed services – operations that change the attributesoperations that change the attributes
multiple attributes – multiple attributes – if it is only one attribute, if it is only one attribute, probably should be part of another classprobably should be part of another class
common attributes – common attributes – common things for all instances of a classcommon things for all instances of a class
common operations – common operations – for all instances of the classfor all instances of the class
essential requirements – essential requirements – appear in the PROBLEM space appear in the PROBLEM space (remember we’re doing analysis modeling!)(remember we’re doing analysis modeling!)
retained information – retained information – information about it must be rememberedinformation about it must be remembered
Coming up: Selecting Classes—Example
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Selecting Classes—Example
needed servicesneeded services
multiple attributesmultiple attributes
common attributescommon attributes
common operationscommon operations
essential requirementsessential requirements
retained informationretained information
Coming up: Elements of the Analysis Model
ATMUser
Yes
Yes
Yes
Yes
Yes
Yes
PinNum
Yes
No
No
Yes
Maybe
Yes
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Use-case diagrams
Use cases - text
Activity Diagrams
Swim lane diagrams
Scenario-based elements
Class diagrams
Analysis Packages
CRC Models
Collaboration Diagrams
Class-based elements
Data-flow diagrams
Control flow diagrams
Processing narratives
Flow-oriented elements
State diagrams
Sequence diagrams
Behavioral elements
Analysis Model
Elements of the Analysis Model
Coming up: Data Modeling
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Data Modeling
examines data objects independently of processing
focuses attention on the data domain creates a model at the customer’s
level of abstraction indicates how data objects relate to
one another
Coming up: What is a Data Object?
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What is a Data Object?
ObjectObject ——something that is described by a setsomething that is described by a setof attributes (data items) and that will be of attributes (data items) and that will be manipulated within the software (system)manipulated within the software (system)
each each instanceinstance of an object (e.g., a book) of an object (e.g., a book) can be identified uniquely (e.g., ISBN #) can be identified uniquely (e.g., ISBN #)
each plays a necessary role in the systemeach plays a necessary role in the systemi.e., the system could not function without i.e., the system could not function without access to instances of the objectaccess to instances of the object
each is described by attributes that are each is described by attributes that are themselves data itemsthemselves data items
What are some typical data objects?
Coming up: Typical Data Objects
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Typical Data Objects
external entitiesexternal entities (printer, user, sensor)(printer, user, sensor)thingsthings (e.g, reports, displays, signals) (e.g, reports, displays, signals) occurrences or eventsoccurrences or events (e.g., interrupt, alarm)(e.g., interrupt, alarm)rolesroles (e.g., manager, engineer, salesperson)(e.g., manager, engineer, salesperson)organizational unitsorganizational units (e.g., division, team)(e.g., division, team)placesplaces (e.g., manufacturing floor) (e.g., manufacturing floor)
structuresstructures (e.g., employee record)(e.g., employee record)
Coming up: Data Objects and Attributes
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Data Objects and AttributesA data object contains a set of attributes that A data object contains a set of attributes that act as an aspect, quality, characteristic, or act as an aspect, quality, characteristic, or descriptor of the objectdescriptor of the object
object: automobileobject: automobileattributes:attributes: makemake modelmodel body typebody type priceprice options codeoptions code
How do data objects differ from OO classes or do they?
Coming up: What is a Relationship?
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What is a Relationship?
relationshiprelationship ——indicates “connectedness”; indicates “connectedness”; a "fact" that must be "remembered" a "fact" that must be "remembered" by the system and cannot or is not computed by the system and cannot or is not computed or derived mechanicallyor derived mechanically
several instances of a relationship can exist objects can be related in many different ways
Coming up: Crow’s Foot Style ERD
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Crow’s Foot Style ERD
Coming up: The ERD: An Example
The ERD: Other style’s exist. There are a few, but most are more confusing and less common than Crow’s foot. Depending on who you ask this was invented by Dr. Gordon Everest of Clive Finkelstein.
Teacher Class
Student Address
Teacher teaches 0 to many classes
Classes have 1 and only 1 teacher
Students have 1 to many addressesAn address is for zero to one student (addresses may not be associated with multiple students)
First “thing” denotes optional or mandatory. Second “thing” denotes cardinality (one or many)
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The ERD: An Example
placesplacesCustomerCustomer
requestrequestfor servicefor service
generatesgenerates workworkorderorder
workworktaskstasks
materialsmaterials
consistsconsistsofof
listslists
(1,1)selectedselected
fromfrom
standardstandardtask tabletask table
Coming up: Elements of the Analysis Model
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Use-case diagrams
Use cases - text
Activity Diagrams
Swim lane diagrams
Scenario-based elements
Class diagrams
Analysis Packages
CRC Models
Collaboration Diagrams
Class-based elements
Data-flow diagrams
Control flow diagrams
Processing narratives
Flow-oriented elements
State diagrams
Sequence diagrams
Behavioral elements
Analysis Model
Elements of the Analysis ModelOnward to data flow diagrams!
Coming up: Flow-Oriented Modeling
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Flow-Oriented Modeling
Represents how data objects are transformed at they Represents how data objects are transformed at they move through the systemmove through the system
A A data flow diagram (DFD)data flow diagram (DFD) is the diagrammatic form that is the diagrammatic form that is usedis used
Considered by many to be an ‘old school’ approach, flow-Considered by many to be an ‘old school’ approach, flow-oriented modeling continues to provide a view of the oriented modeling continues to provide a view of the system that is unique—it should be used to supplement system that is unique—it should be used to supplement other analysis model elementsother analysis model elements
Coming up: The Flow Model
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The Flow Model
Every computer-based system is an Every computer-based system is an information transform ....information transform ....
computercomputerbasedbased
systemsysteminputinput outputoutput
Coming up: Flow Modeling Notation
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Flow Modeling Notation
external entityexternal entity
processprocess
data flowdata flow
data storedata store
Coming up: External Entity
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External Entity
A producer or consumer of dataA producer or consumer of data
Examples: a person, a device, a sensorExamples: a person, a device, a sensor
Another example: computer-basedAnother example: computer-basedsystemsystem
Data must always originate somewhereData must always originate somewhereand must always be sent to somethingand must always be sent to something
Coming up: Process
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Process
A data transformer (changes inputA data transformer (changes inputto output)to output)
Examples: compute taxes, determine area,Examples: compute taxes, determine area,format report, display graph format report, display graph
Data must always be processed in some Data must always be processed in some way to achieve system functionway to achieve system function
Coming up: Data Flow
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Data Flow
Data flows through a system, beginningData flows through a system, beginningas input and be transformed into output.as input and be transformed into output.
computecomputetriangle triangle
areaarea
basebase
heightheight
areaarea
Coming up: Data Stores
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Data Stores
DataData is often stored for later use.is often stored for later use.
look-uplook-upsensorsensor
datadata
sensor #sensor #
report requiredreport required
sensor #, type, sensor #, type, location, agelocation, age
sensor datasensor data
sensor numbersensor number
type, type, location, agelocation, age
Coming up: Data Flow Diagramming:Guidelines
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Data Flow Diagramming:Guidelines
all icons must be labeled with meaningful names
the DFD evolves through a number of levels of detail
always begin with a context level diagram (also called level 0)
always show external entities at level 0 always label data flow arrows do not represent procedural logic
Coming up: Constructing a DFD—I
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Constructing a DFD—I
review the data model to isolate data objects and use a grammatical parse to determine “operations”
determine external entities (producers and consumers of data)
create a level 0 DFD
Coming up: Level 0 DFD Examples
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Level 0 DFD Examplesuseruser
processing processing requestrequest
videovideosourcesource NTSCNTSC
video signalvideo signal
digitaldigitalvideovideo
processorprocessor
requestedrequestedvideovideosignalsignal
monitormonitor
Coming up: Constructing a DFD—II
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Constructing a DFD—II
write a narrative describing the transform
parse to determine next level transforms
“balance” the flow to maintain data flow continuity
develop a level 1 DFD use a 1:5 (approx.) expansion ratio
Coming up: The Data Flow Hierarchy
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The Data Flow Hierarchy
PPaa bbxx yy
p1p1p2p2
p3p3p4p4 55
aa
bb
cc
ddee
ff
gg
level 0level 0
level 1level 1
Coming up: Example DFD: Level 1
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Example DFD: Level 1
Coming up: DFD: A practical example
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DFD: A practical example
Launched Dec. 11, 1998, the Climate Orbiter plunged too steeply into the Martian atmosphere Sept. 23, 1999, and either burned up or crashed. In an initial failure report released Oct. 15, 2000 the review board blamed the navigation error on a communications foul-up between NASA's Jet Propulsion Laboratory and prime contractor Lockheed Martin.
Launched Dec. 11, 1998, the Climate Orbiter plunged too steeply into the Martian atmosphere Sept. 23, 1999, and either burned up or crashed. In an initial failure report released Oct. 15, 2000 the review board blamed the navigation error on a communications foul-up between NASA's Jet Propulsion Laboratory and prime contractor Lockheed Martin.
Collect,analyze,
generate flightcontrol data
JPL-1
J1 JPL store
Convert datafrom Metric to
English
?
LM1 LM store
Controlspaceflight
LM-1
English data
Transfer of Flight Control DataThis processwas missing
Metric data
Transfer data
?
Who wasresponsible
for this task?
Coming up: Lets Try It
Lets Try It
Lets create a DFD for A carpet cleaning business A web-based order processing system for a
computer store An address book for an iPhone
Coming up: Flow Modeling Notes
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Flow Modeling Notes
each bubble is refined until it does just one thing
the expansion ratio decreases as the number of levels increase
most systems require between 3 and 7 levels for an adequate flow model
a single data flow item (arrow) may be expanded as levels increase (data dictionary provides information)
Coming up: Elements of the Analysis Model
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Use-case diagrams
Use cases - text
Activity Diagrams
Swim lane diagrams
Scenario-based elements
Class diagrams
Analysis Packages
CRC Models
Collaboration Diagrams
Class-based elements
Data-flow diagrams
Control flow diagrams
Processing narratives
Flow-oriented elements
State diagrams
Sequence diagrams
Behavioral elements
Analysis Model
Elements of the Analysis Model
Oh behave!
Coming up: Behavioral Modeling
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Behavioral Modeling The behavioral model indicates how software will
respond to external events or stimuli. To create the model, the analyst must perform the following steps:
Evaluate all use-cases to fully understand the sequence of interaction within the system.
Identify events that drive the interaction sequence and understand how these events relate to specific objects.
Create a sequence diagram for each use-case. Build a state diagram for the system. Review the behavioral model to verify accuracy and
consistency.
Coming up: State Representations
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State Representations
In the context of behavioral modeling, two different characterizations of states must be considered: the state of each class as the system performs its function
and the state of the system as observed from the outside as the
system performs its function
Coming up: State Diagram for the ControlPanel Class
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State Diagram for the ControlPanel Class
reading
locked
selecting
passwordentered
comparing
password = incorrect& numberOfTries < maxTries
password = correct
activation successful
key hit
do: validatePassword
numberOfTries > maxTries
timer < lockedTime
timer > lockedTime
Coming up: State Diagram Details
State Diagram Details
Coming up: The States of a System
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State Name (verb in current tense)
(Optional) actions happening during state
Name Examples:sortingvalidatingupdating status…
[age > 20]
[age <= 20]
Guards: Use to describe event that causes a state transition happens (ALL transitions should have guards)
[age <= 20]/setFlag(false)
Action: If something happens while transitioning to another state. (Optional)
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The States of a System state—a set of observable
circumstances that characterizes the behavior of a system at a given time
state transition —the movement from one state to another
event —an occurrence that causes the system to exhibit some predictable form of behavior
action —process that occurs as a consequence of making a transition
Coming up: Behavioral Modeling
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Behavioral Modeling
make a list of the different states of a system (How does the system behave?)
indicate how the system makes a transition from one state to another (How does the system change state?) indicate event indicate action
draw a state diagram or a sequence diagram
Coming up: State Diagram - Lets Try It!
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State Diagram - Lets Try It!You are designing a traffic light system for this intersection.
Draw a state diagram showing the different states and how they transition.
North
South
East
West
Coming up: Elements of the Analysis Model
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Use-case diagrams
Use cases - text
Activity Diagrams
Swim lane diagrams
Scenario-based elements
Class diagrams
Analysis Packages
CRC Models
Collaboration Diagrams
Class-based elements
Data-flow diagrams
Control flow diagrams
Processing narratives
Flow-oriented elements
State diagrams
Sequence diagrams
Behavioral elements
Analysis Model
Elements of the Analysis Model
Coming up: Object Oriented Analysis (OOA)
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Object Oriented Analysis (OOA)
The intent of OOA is to define all classes (and the relationships and behavior associated with them) that are relevant to the problem to be solved. For that, a number of tasks must occur:
1. Classes must be identified (i.e., attributes and methods)
2. A class hierarchy is defined
3. Object-to-object relationships should be represented
4. Object behavior must be modeled
5. Tasks 1 through 4 are reapplied iteratively
Coming up: Object-Oriented Concepts
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Object-Oriented Concepts What are the basic object oriented
concepts?
Coming up: Object-Oriented Concepts
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Object-Oriented Concepts What are the basic object oriented
concepts? Classes and objects Attributes and operations Encapsulation and instantiation Inheritance
The analysis model is designed to help you make “good” choices
Coming up: Object-Oriented Concepts
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Object-Oriented Concepts What helps you determine if
something should be a class or an attribute?
What helps you determine needed operations?
How does the analysis model make sure your requirements are correct?
Coming up: Elements of the Analysis Model
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Elements of the Analysis ModelScenario-based elements
Class-based elements
Flow-oriented elements
Behavioral elements
Coming up: Analysis Model Rules of Thumb
High level idea of the system from user’s or a functional perspective
How information flows throughout the system (data and control flow)
How the system responds to external stimuli
Static view of the system and how the different parts are related. Tries to show standard ideas of object oriented development
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Analysis Model Rules of Thumb
The model should focus on requirements that are visible within the problem or business domain. The level of abstraction should be relatively high.
Each element of the analysis model should add to an overall understanding of software requirements and provide insight into the information domain, function and behavior of the system.
Delay consideration of infrastructure and other non-functional models until design.
Minimize coupling throughout the system. Be certain that the analysis model provides value to all
stakeholders. Keep the model as simple as it can be.
Coming up: Analysis Phase: What is it?
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Analysis Phase: What is it?
systemdescription
analysismodel
designmodel
Three objectives:
• To describe what the customer requires
• To establish a basis for the creation of a software design
• To define a set of requirements that can be validated once the software is built
Three objectives:
• To describe what the customer requires
• To establish a basis for the creation of a software design
• To define a set of requirements that can be validated once the software is built
Coming up: Writing the Software Specification
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Writing the Software Specification
Everyone knew exactly what had to be done until someone wrote it down!
Coming up: Specification Guidelines
Read the last three
slides on your own
Read the last three
slides on your own
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Specification Guidelinesuse a layered format that provides increasing detail as the "layers" deepen
use consistent graphical notation and apply textual terms consistently (stay away from aliases)
be sure to define all acronyms
be sure to include a table of contents; ideally, include an index and/or a glossary
write in a simple, unambiguous style (see "editing suggestions" on the following pages)
always put yourself in the reader's position, "Would I be able to understand this if I wasn't intimately familiar with the system?"
Coming up: Specification Guidelines
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Specification GuidelinesBe on the lookout for persuasive connectors, ask why? keys: certainly, therefore, clearly, obviously, it follows that ...
Watch out for vague terms keys: some, sometimes, often, usually,ordinarily, most, mostly ...
When lists are given, but not completed, be sure all items are understood keys: etc., and so forth, and so on, such as
Be sure stated ranges don't contain unstated assumptions e.g., Valid codes range from 10 to 100. Integer? Real? Hex?
Beware of vague verbs such as handled, rejected, processed, ...
Beware "passive voice" statements e.g., The parameters are initialized. By what?
Beware "dangling" pronouns e.g., The I/O module communicated with the data validation module and its contol flag is set. Whose control flag?
Coming up: Specification Guidelines
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Specification GuidelinesWhen a term is explicitly defined in one place, try substituting the definition forother occurrences of the term
When a structure is described in words, draw a picture
When a structure is described with a picture, try to redraw the picture to emphasize different elements of the structure
When symbolic equations are used, try expressing their meaning in words
When a calculation is specified, work at least two examples
Look for statements that imply certainty, then ask for proof keys; always, every, all, none, never
Search behind certainty statements—be sure restrictions or limitations are realistic
End of presentation