Page 1
Software Engineering Research Group: Processes and MeasurementFachbereich InformatikTU Kaiserslautern
Grundlagen des Software EngineeringFundamentals of Software Engineering
Winter Term 2011/12
Prof. Dr. Dr. h. c. Dieter Rombach
Chapter 4.2:
Software Application Engineering – Requirements Engineering for Embedded Systems
Last update: 21/11/2011
Page 2
� Embedded Systems (ES)�Characteristics
�Req. Categories
�Properties
� Requirement Specification for ES�4 Variables model
�Sequence Based Specification
�Software Cost Reduction
© Prof. Dr. Dr. h. c. Dieter Rombach, Fundamentals of Software Engineering, Winter Term 2011/12 1
AE – RE for Embedded Systems
Goals
� The goals of this chapter are to be able to
– characterize embedded systems (ES)
– identify and define issues relevant for engineering ES
– identify requirements categories for ES
– Use a simple model for documenting functional ES requirements
� Literature
– David Parnas and Jan Madey. Functional Documents for Computer Science. Science of Computer Programming, Elsevier, 1995“
– Stacy J. Prowell, Carmen J. Trammell, Richard C. Linger, and Jesse H. Poore. 1999. Cleanroom Software Engineering: Technology and Process. Addison-Wesley Longman Publishing Co., Inc., Boston, MA, USA.
Page 3
� Embedded Systems (ES)�Characteristics
�Req. Categories
�Properties
� Requirement Specification for ES�4 Variables model
�Sequence Based Specification
�Software Cost Reduction
© Prof. Dr. Dr. h. c. Dieter Rombach, Fundamentals of Software Engineering, Winter Term 2011/12 3
AE – RE for Embedded Systems
Characteristics
� Interaction
– With User – always?
– With environment – always!
� Complex functionality
– Specific tasks (does not imply trivial !!)
� Limited memory
� Application specific control logic
– Special hardware (ASIC/ FPGA/ Microcontroller)
� Low power
– Often battery operated (autonomous)
– Power issues (heat management)
� Low manufacturing cost (mass products)
Page 4
� Embedded Systems (ES)�Characteristics
�Req. Categories
�Properties
� Requirement Specification for ES�4 Variables model
�Sequence Based Specification
�Software Cost Reduction
© Prof. Dr. Dr. h. c. Dieter Rombach, Fundamentals of Software Engineering, Winter Term 2011/12 4
AE – RE for Embedded Systems
Requirements categories
� Functional
– Domain-dependent
– User-dependent
� Non-functional
– Performance �
– Resource consumption (e.g., power)
– Dependability
→ Safety �
→ Reliability �
→ Availability �
→ Maintainability ?
→ Integrity ?
� Inverse
– All safety critical issues
� (Design Constraints)
Page 5
� Embedded Systems (ES)�Characteristics
�Req. Categories
�Properties
� Requirement Specification for ES�4 Variables model
�Sequence Based Specification
�Software Cost Reduction
© Prof. Dr. Dr. h. c. Dieter Rombach, Fundamentals of Software Engineering, Winter Term 2011/12 5
AE – RE for Embedded Systems
Some example properties of interest in software for ES
� Functional
– Real-time (soft � hard!): Button X is pressed � do task in deadline s.
– Response to external events (event-driven/reactive): Button X is pressed � do task
– Temporal: safety and liveness
→ Safety: Something bad will never happen
→ Liveness: Something good will eventually happen.
– Communication and concurrency
– Heterogeneity
� Non-functional
– Performance: Component X processes Y requests / hour
– Resources: Available memory is 128 KB
– Dependability: Failure rate of the component ≤ 10-4 failures / month
� E.g., Fault tolerance ?
– Is this really a property / requirement?
– A means for achieving higher dependability
→ Other means include prevention, removal and forecasting
– However, fault tolerance is often needed e.g., networked ES
Page 6
� Embedded Systems (ES)�Characteristics
�Req. Categories
�Properties
� Requirement Specification for ES�4 Variables model
�Sequence Based Specification
�Software Cost Reduction
© Prof. Dr. Dr. h. c. Dieter Rombach, Fundamentals of Software Engineering, Winter Term 2011/12 6
AE – RE for Embedded Systems
Requirement Specification for ES- A closer look at an ES
CMOS Light(Sensor)
Electronic shutter
(Actuator)
Microcontroller / Microprocessor
Memory(Software )
A/D (D/A) conversion
ASIC / FPGA
Page 7
� Embedded Systems (ES)�Characteristics
�Req. Categories
�Properties
� Requirement Specification for ES�4 Variables model
�Sequence Based Specification
�Software Cost Reduction
© Prof. Dr. Dr. h. c. Dieter Rombach, Fundamentals of Software Engineering, Winter Term 2011/12 7
AE – RE for Embedded Systems
Requirement Specification for ES- A closer look to an ES: Block diagram
Sensor
Actuators
D/A
Control Logic
(Hardware +Software)
System input
System output
A/D
Page 8
� Embedded Systems (ES)�Characteristics
�Req. Categories
�Properties
� Requirement Specification for ES�4 Variables model
�Sequence Based Specification
�Software Cost Reduction
© Prof. Dr. Dr. h. c. Dieter Rombach, Fundamentals of Software Engineering, Winter Term 2011/12 8
AE – RE for Embedded Systems
Requirement Specification for ES- A closer look to an ES: Block diagram
� How do we begin?
– Identify system boundary
→ Interfaces
� Input
� Output
– Define what is true at system boundary
→ Relation between input and output
– Define constraints on the system
→ Also a relation between input and output
Page 9
� Embedded Systems (ES)�Characteristics
�Req. Categories
�Properties
� Requirement Specification for ES�4 Variables model
�Sequence Based Specification
�Software Cost Reduction
© Prof. Dr. Dr. h. c. Dieter Rombach, Fundamentals of Software Engineering, Winter Term 2011/12 9
AE – RE for Embedded Systems
Requirement Specification for ES- Logical model
Sensor
Actuators
D/A
Control Logic
(Hardware +Software)
Monitored valuem(t)
Controlled valuec(t)
A/D
O(t)i(t)
Input device
Output device
Page 10
� Embedded Systems (ES)�Characteristics
�Req. Categories
�Properties
� Requirement Specification for ES�4 Variables model
�Sequence Based Specification
�Software Cost Reduction
© Prof. Dr. Dr. h. c. Dieter Rombach, Fundamentals of Software Engineering, Winter Term 2011/12 10
AE – RE for Embedded Systems
� System requirements document
– Black-box view of the system
– Description of the environment
→ Constraints from the environment e.g., physical laws
– Constraints relevant for the system to be built
– Assumptions
� Document whose content is defined by mathematical r elations
� Before we continue, Elementary set-theoretic concep ts:
– Relation
→ AH: Set of {Age, Height}: {{20, 170}, {25,170}, {30,180}, {35,185}}
– Function
→ NA: Set of {Name, Age}: {{A, 20}, {B, 25}, {C, 30}, {D, 35}}
→ A well-behaved relation
– Domain
→ For a function f or a relation r domain Dom ( f) or Dom (r) : X-values
→ Dom (AH): {20, 25, 30, 35}
– Range
→ For a function f or a relation r range Ran (f) or Ran (r) : Y-values
→ Ran(NA): {20, 25, 30, 35}
Page 11
� Embedded Systems (ES)�Characteristics
�Req. Categories
�Properties
� Requirement Specification for ES�4 Variables model
�Sequence Based Specification
�Software Cost Reduction
© Prof. Dr. Dr. h. c. Dieter Rombach, Fundamentals of Software Engineering, Winter Term 2011/12 11
AE – RE for Embedded Systems
4 Variables model
SOFMonitored valuem i(t)
Controlled valuec i(t)
Oi(t)
i i(t)
Sensor
Input device
Actuators
Output device
Logical System boundary REQ
Page 12
� Embedded Systems (ES)�Characteristics
�Req. Categories
�Properties
� Requirement Specification for ES�4 Variables model
�Sequence Based Specification
�Software Cost Reduction
© Prof. Dr. Dr. h. c. Dieter Rombach, Fundamentals of Software Engineering, Winter Term 2011/12 12
AE – RE for Embedded Systems
4 Variables model- Monitored and Controlled variables
� Characteristics
– Monitored variables: (Sensor) Variables whose values influence output of the machine / system
– Controlled variables: (Actuator) Variables whose values are determined by the system
– Exist (are visible) outside the system boundary
→ Often physical quantities
– Values often vary with time
� Mathematically
– Monitored variables m i(t)
→ m(t): R � Value
� “m”: function assigning a time dependent real value.
→ M(t) : {m1(t), m2(t), …, mn(t)} : Vector of monitored variables
– Controlled variables c i(t)
→ c(t): R � Value
� “c” : function assigning a time dependent real value.
→ C(t) : {c1(t), c2(t), …, cn(t)} : Vector of controlled variables
Page 13
� Embedded Systems (ES)�Characteristics
�Req. Categories
�Properties
� Requirement Specification for ES�4 Variables model
�Sequence Based Specification
�Software Cost Reduction
© Prof. Dr. Dr. h. c. Dieter Rombach, Fundamentals of Software Engineering, Winter Term 2011/12 13
AE – RE for Embedded Systems
4 Variables model- Input and Output variables
� Input variables– Input variables ii(t)
→ Variables whose values are the result of measurement of mi(t)– Output variables oi(t)
→ Variables whose values are the result of computation by the machine
� For all ( ∀∀∀∀) m i(t) there exists ( ∃∃∃∃) a corresponding i i(t)� ∀∀∀∀ c i(t) ∃∃∃∃ o i(t)
– Vice-versa need not be true– Often ii(t) and oi(t) will be discrete and digital
→ If the machine is HW/SW control logic
Page 14
� Embedded Systems (ES)�Characteristics
�Req. Categories
�Properties
� Requirement Specification for ES�4 Variables model
�Sequence Based Specification
�Software Cost Reduction
© Prof. Dr. Dr. h. c. Dieter Rombach, Fundamentals of Software Engineering, Winter Term 2011/12 14
AE – RE for Embedded Systems
4 Variables model- Relations
� NATural constraints expressed as a relation between the vectors of monitored variables M(t) and controlled variables C(t)
– Dom (NAT): values of M(t) – Ran (NAT): values of C(t) – {M(t), C(t)} ∈ NAT if and only if (iff) environment (nature) permits the behavior
� REQuirements specified as a relation between the vec tors of monitored variables M(t) and controlled variables C(t)
– Dom (REQ): values of M(t) – Ran (REQ): values of C(t) – {M(t), C(t)} ∈ REQ iff system should permit the behavior
� INput device description is a relation between monit ored variables M(t) and Input variables I(t)
� OUTput device description is a relation between outp ut variables O(t) and controlled variables C(t)
� SOFtware requirements specified as a relation betwee n Input variables I(t) and output variables O(t)
– Dom (SOF): values of I(t) – Ran (SOF): values of O(t) – {I(t), O(t)} ∈ SOF iff software should permit the behavior
Page 15
� Embedded Systems (ES)�Characteristics
�Req. Categories
�Properties
� Requirement Specification for ES�4 Variables model
�Sequence Based Specification
�Software Cost Reduction
© Prof. Dr. Dr. h. c. Dieter Rombach, Fundamentals of Software Engineering, Winter Term 2011/12 15
AE – RE for Embedded Systems
4 Variables model- Properties
� This should ALWAYS be true– Dom (REQ) ⊇⊇⊇⊇ (is a subset of) Dom (NAT) or document is incomplete– If (Dom (NAT ∩∩∩∩ REQ) = Dom (NAT) ∩∩∩∩ Dom (REQ)) also holds then REQ is
considered feasible with respect to NATElse system breaks laws of nature
� Software behavior is acceptable if
∀∀∀∀ M(t), C(t), I(t), O(t) [IN(M(t), I(t)) & SOF(I(t),O(t)) & OUT(O(t), C(t)) & NAT(M(t), C(t)) ]
→ REQ(M(t), C(t) )
Page 16
� Embedded Systems (ES)�Characteristics
�Req. Categories
�Properties
� Requirement Specification for ES�4 Variables model
�Sequence Based Specification
�Software Cost Reduction
© Prof. Dr. Dr. h. c. Dieter Rombach, Fundamentals of Software Engineering, Winter Term 2011/12 16
AE – RE for Embedded Systems
4 Variables model- Summary
MON CON
INPUT OUTPUT
NAT
REQ
SOF
IN OUT
Page 17
� Embedded Systems (ES)�Characteristics
�Req. Categories
�Properties
� Requirement Specification for ES�4 Variables model
�Sequence Based Specification
�Software Cost Reduction
© Prof. Dr. Dr. h. c. Dieter Rombach, Fundamentals of Software Engineering, Winter Term 2011/12 17
AE – RE for Embedded Systems
4 Variables models
� We now know:
– What to document in an system requirement specification of embedded systems
– What properties it must satisfy
→ Completeness, feasibility, acceptability (of software)
– Abstraction
� How do we go about documenting this?
– Natural language
→ Common practice
→ Can be imprecise and ambiguous
– Critical systems demand usage of formalized notation where syntax and semantics are precisely defined
– Known example
→ SBS
→ Software cost reduction
Page 18
� Embedded Systems (ES)�Characteristics
�Req. Categories
�Properties
� Requirement Specification for ES�4 Variables model
�Sequence Based Specification
�Software Cost Reduction
© Prof. Dr. Dr. h. c. Dieter Rombach, Fundamentals of Software Engineering, Winter Term 2011/12 18
AE – RE for Embedded Systems
Sequence Based Specification
� Tag requirements
� Define system boundary
– Identify stimuli
– Identify responses
– Choice of appropriate abstraction
→ Stimuli and responses could change depending on the level of abstraction
� Systematic enumeration of Stimuli Sequence � Response and Stimuli Sequenceequivalence
Page 19
� Embedded Systems (ES)�Characteristics
�Req. Categories
�Properties
� Requirement Specification for ES�4 Variables model
�Sequence Based Specification
�Software Cost Reduction
© Prof. Dr. Dr. h. c. Dieter Rombach, Fundamentals of Software Engineering, Winter Term 2011/12 19
AE – RE for Embedded Systems
Sequence Based Specification
� Tag requirements
Tag Requirements
1The security alarm has a detector that sends a trip signal when motion is detected
2 The security alarm is activated by pressing the SET button
3 The SET button is illuminated when the security alarm is set
4If a trip signal occurs while the security alarm is set, a tone (alarm) is emitted
5 A three-digit code must be entered to silence the alarm tone
6 Correct entry of the code deactivates the security alarm
7If a mistake is made when entering the code, the user must press the CLEAR button before the code can be reentered
Page 20
� Embedded Systems (ES)�Characteristics
�Req. Categories
�Properties
� Requirement Specification for ES�4 Variables model
�Sequence Based Specification
�Software Cost Reduction
© Prof. Dr. Dr. h. c. Dieter Rombach, Fundamentals of Software Engineering, Winter Term 2011/12 20
AE – RE for Embedded Systems
Sequence Based Specification
� Define system boundary
– Identify stimuli
– Identify responses
Stimulus Description Symbol Trace
Set Device activator S 2
Trip Signal from detector T 1
BadDigitIncorrect entry of a digit in thecode
B 7
Clear Clear entry C 7
GoodDigit
A digit that is part of thecorrect entry of the 3-digitcode that deactivates the alarmand the device
G 5,6
Response Description Trace
Light On Set button illuminated 3
Light Off Set button not illuminated 6
Alarm On Alarm tone activated 4
Alarm Off Alarm tone deactivated 5
Page 21
� Embedded Systems (ES)�Characteristics
�Req. Categories
�Properties
� Requirement Specification for ES�4 Variables model
�Sequence Based Specification
�Software Cost Reduction
© Prof. Dr. Dr. h. c. Dieter Rombach, Fundamentals of Software Engineering, Winter Term 2011/12 21
AE – RE for Embedded Systems
Sequence Based Specification
� Systematic enumeration of Stimuli Sequence � Response and Stimuli Sequence equivalence
– Rule:
→ Do not extend the sequence IF
� the response is “illegal” OR IF
� the sequence is declared equivalent to a previous sequence
� ELSE extend
– Sequences of length 0 and 1
– Derived requirements
Sequence Response Equivalence Trace
λ (empty) null D1
S Light On 2, 3
T Illegal D1
B Illegal D1
C Illegal D1
G Illegal D1
D1 The security alarm is initially deactivated
Page 22
� Embedded Systems (ES)�Characteristics
�Req. Categories
�Properties
� Requirement Specification for ES�4 Variables model
�Sequence Based Specification
�Software Cost Reduction
© Prof. Dr. Dr. h. c. Dieter Rombach, Fundamentals of Software Engineering, Winter Term 2011/12 22
AE – RE for Embedded Systems
Sequence Based Specification
� Systematic enumeration of Stimuli Sequence � Response and Stimuli Sequenceequivalence
– Sequences of length 2
Sequence Response Equivalence Trace
SS null S D2
ST Alarm On 4
SB null D3
SC null S D4
SG null D5
D2After the device has been set, the Set button has no further effect until the device has been deactivated
D3 The device produces no external response to an erroneous entry
D4 The device produces no external response to a Clear entry
D5The device produces no external response to correct entry of a GoodDigit until all three digits of the code have been entered
Page 23
� Embedded Systems (ES)�Characteristics
�Req. Categories
�Properties
� Requirement Specification for ES�4 Variables model
�Sequence Based Specification
�Software Cost Reduction
© Prof. Dr. Dr. h. c. Dieter Rombach, Fundamentals of Software Engineering, Winter Term 2011/12 23
AE – RE for Embedded Systems
Sequence Based Specification
� Systematic enumeration of Stimuli Sequence � Response and Stimuli Sequenceequivalence
– Rule:
→ The enumeration is complete if there are no more sequences to extend
– Sequences of length 5
Sequence Response Equivalence Trace
STGGS null STGG D2
STGGT null STGG D6
STGGB null STB D3
STGGC null ST D4
STGGGAlarm OffLight Off
λ 3, 5, 6
Page 24
� Embedded Systems (ES)�Characteristics
�Req. Categories
�Properties
� Requirement Specification for ES�4 Variables model
�Sequence Based Specification
�Software Cost Reduction
© Prof. Dr. Dr. h. c. Dieter Rombach, Fundamentals of Software Engineering, Winter Term 2011/12 24
AE – RE for Embedded Systems
Software cost reduction (SCR)
� Developed at the US Naval Research Labs during the development of the A-7 aircraft
– Tabular representation of state changes
– Uses 2 of the relations from the 4 variable model (NAT, REQ)
– Synchronous model
→ One set of inputs processed in a state before processing the inputs at next state
– One input assumption
→ Only one input changes at a time
MON MON
INPUT OUTPUT
NAT
REQ
SOF
IN OUT
SCR mainly deals with this part
Page 25
� Embedded Systems (ES)�Characteristics
�Req. Categories
�Properties
� Requirement Specification for ES�4 Variables model
�Sequence Based Specification
�Software Cost Reduction
© Prof. Dr. Dr. h. c. Dieter Rombach, Fundamentals of Software Engineering, Winter Term 2011/12 25
AE – RE for Embedded Systems
Elements of the SCR model
� System is a state machine (S, S 0, Em,T) consisting of
– States S, initial state S0
– Em : set of monitored events
– T : allowable transitions
→ Function mapping monitored event (e ∈ Em) and the current state (s ∈ S) to the next state (s’ ∈ S)
� System mode class: An equivalence class of system s tates (a set of states)
– Values of a mode class are called modes
� Condition: Predicate defined on a single system state
– Predicate is often a Boolean-valued function
� Event: Predicates on two system states
� Occurrence: An event occurs if a condition changes
� Conditioned event: @T(c) WHEN d
� @T(c): @T(c) WHEN TRUE: c becomes True
� @F(c): @T(c) WHEN FALSE : c becomes False
Page 26
� Embedded Systems (ES)�Characteristics
�Req. Categories
�Properties
� Requirement Specification for ES�4 Variables model
�Sequence Based Specification
�Software Cost Reduction
© Prof. Dr. Dr. h. c. Dieter Rombach, Fundamentals of Software Engineering, Winter Term 2011/12 26
AE – RE for Embedded Systems
Types of SCR tables
� Variable Tables: Definition of monitored & controlled variable values
� Mode Condition Table: Definition of modes based on monitored variables
� Mode Transition Table: Mode transitions described as a function of current mode and monitored variables
– i.e. (conditioned) monitored events
� Event Table: Definition of values of a controlled variable given (conditioned) monitored events and modes
Functions should be total i.e. defined for all poss ible inputs
Page 27
� Embedded Systems (ES)�Characteristics
�Req. Categories
�Properties
� Requirement Specification for ES�4 Variables model
�Sequence Based Specification
�Software Cost Reduction
© Prof. Dr. Dr. h. c. Dieter Rombach, Fundamentals of Software Engineering, Winter Term 2011/12 27
AE – RE for Embedded Systems
Software Cost Reduction
mSetmTripmNumber[1,2,3]mClear
ClightcAlarm
I O
Req
Sof
SW-System
mVar cVar
System
Page 28
� Embedded Systems (ES)�Characteristics
�Req. Categories
�Properties
� Requirement Specification for ES�4 Variables model
�Sequence Based Specification
�Software Cost Reduction
© Prof. Dr. Dr. h. c. Dieter Rombach, Fundamentals of Software Engineering, Winter Term 2011/12 28
AE – RE for Embedded Systems
Variable tables – monitored variables
mSet
Event / Condition Values
Initial OR
@T(!3 correct digits entered!) when mSet=$on$
$off$
@T(!user pushes setButton!) $on$
mTrip
Event / Condition Values
@T(!motion_detected)when mTrip = $off$
$on$
Initial OR @T(!3 correct digits entered!)
when mTrip = $on$$off$
mNumber[i=1..3]
Event / Condition Values
Initial OR
@F(!user pushes the right digit number i!)
$F$
@T(!user pushes the right digit number i!)
$T$
mClear
Event / Condition Values
@T(!user pushes clear button!)
when mSet = $on$$on$
Initial OR
@T(!user entered a digit!)$off$
Page 29
� Embedded Systems (ES)�Characteristics
�Req. Categories
�Properties
� Requirement Specification for ES�4 Variables model
�Sequence Based Specification
�Software Cost Reduction
© Prof. Dr. Dr. h. c. Dieter Rombach, Fundamentals of Software Engineering, Winter Term 2011/12 29
AE – RE for Embedded Systems
Variable tables – controlled variables
cLight
Event / Condition Values
Initial OR
@T(mSet = $off$)$off$
@T(mSet=$on$) $on$
cAlarm
Event / Condition Values
Initial OR
i=1,2,3: mNumber[i] = $T$$off$
@T(mTrip=$on$) when $mSet$ = $on$
$on$
Page 30
� Embedded Systems (ES)�Characteristics
�Req. Categories
�Properties
� Requirement Specification for ES�4 Variables model
�Sequence Based Specification
�Software Cost Reduction
© Prof. Dr. Dr. h. c. Dieter Rombach, Fundamentals of Software Engineering, Winter Term 2011/12 30
AE – RE for Embedded Systems
Contition table
� Describe Modes (= externally visible states)
– Informal
– Mode condition table
� Example of a mode condition table:
mode condition
*off* mSet = $off$
*on* mSet = $on$ AND
- *passive* mTrip = $off$ AND
- *pas_0*
- *pas_1* mNumber[1] = $T$
- *pas_2* mNumber[2] = $T$
- *active* mTrip = $on$ AND
- *act_0*
- *act_1* mNumber[1] = $T$
- *act_2* mNumber[2] = $T$
Page 31
� Embedded Systems (ES)�Characteristics
�Req. Categories
�Properties
� Requirement Specification for ES�4 Variables model
�Sequence Based Specification
�Software Cost Reduction
© Prof. Dr. Dr. h. c. Dieter Rombach, Fundamentals of Software Engineering, Winter Term 2011/12 31
AE – RE for Embedded Systems
Mode transition table
� Describe Mode transitions
– Informal
– Mode transition matrix
� Example of mode transition matrix (automobile):
inputmode
output mode
* off * * inactive * …
* off *@T(ignitio
nVar = $on§)
…
* inactive *@F(ignitio
nVar =$on$)
… …
… … … …
Page 32
� Embedded Systems (ES)�Characteristics
�Req. Categories
�Properties
� Requirement Specification for ES�4 Variables model
�Sequence Based Specification
�Software Cost Reduction
© Prof. Dr. Dr. h. c. Dieter Rombach, Fundamentals of Software Engineering, Winter Term 2011/12 32
AE – RE for Embedded Systems
Mode transition table
I / O *off* * act_0 * *act_1* *act_2* *pas_0* *pas_1* *pas _2*
*off* @T(mSet = $on$)
*act_0* @T(mNumber[1] = $T$)
*act_1* @T(mNumber[1] = $F$) OR @T(mClear=$on$)
@T(mNumber[2] = $T$)
*act_2* @T(mNumber[2] = $T$)
@T(mNumber[2] = $F$) OR @T(mClear=$on$)
*pas_0* @T(mTrip = $on$)
@T(mNumber[1] = $T$)
*pas_1* @T(mTrip = $on$)
@T(mClear=$on$)
@T(mNumber[2] = $T$)
*pas_2* @T(mNumber[3] = $T$)
@T(mTrip = $on$)
@T(mClear=$on$)
Page 33
� Embedded Systems (ES)�Characteristics
�Req. Categories
�Properties
� Requirement Specification for ES�4 Variables model
�Sequence Based Specification
�Software Cost Reduction
© Prof. Dr. Dr. h. c. Dieter Rombach, Fundamentals of Software Engineering, Winter Term 2011/12 33
AE – RE for Embedded Systems
Event table
� Give time-independent specification of the sw funct ion
Mode Conditions
*X* Cond 1 Cond 2 Cond 3
*automaticon*
!too slow! …. …
cAccelerate
!increasespeed!
….. …..
mode Conditions
*off*
*pas_0*
*pas_1*
*pas_2*
*act_0*
*act_1*
*act_2*
---
T
T
T
T
T
T
T
---
---
---
---
---
---
---
---
---
---
T
T
T
T
T
T
T
---
---
---
cLight $on$ $off$
cAlarm $on$ $off$