Problem Frames 8 - Variant frames

Problem Frames 8 - Variant frames

Variants

• Model

• Operator

• Description

• Connection

• Control

Operator• Commanded Behavior is the operator

variant of Controlled Behavior

Control machine

Operator

C

B E4RM!E2

C3

CommandedBehavior

Control machine

ControlDomain

C

CD!C2

C3 RequiredBehavior

CM!C1

ControlDomain

CM!C1

CD!C2

Commanded Information

Answering machine

Operator

C

B

Y4

Op!E5

C2

CommandedInformation

DisplayAM!E3

RW!C1

C

Real World

E5

Commanded Workpiece?

Weird machine

Operator

B

B

E3

Op!E5

Y4

CommandedBehaviorUser

US!E3

WM!E1

X

Work Pieces

E5

WP!Y2

Concern of operator variant

• Reject commands that are not sensible or not viable

• Carry out commands that are sensible and viable

Description variant

• Model variant makes a lexical domain that describes part of a domain

• Description variant makes a lexical domain that describes part of the requirement

• Description domain is a set of rules that machine will interpret

• A virtual machine!

Regulated One Way Lights

Regulated Controller

C

ER!{Phase,Duration}ER!{Char}

LU! {Go(I),Stop(I)}Conformity to regime

Light Units

RC! {Rpule(I),Gpulse(I)}

Encoded regime

LU! {Go(I),Stop(I)}

Device Failure Detection

Failure Detector C

Report AD failure

ICU Patients

Patient Constraints

C

Failure Report

C

Analog devices

Description Concern

• Must design description

• Requirements defines how to interpret description

• How does machine get new description?– Often there is another machine that edits it

Connection variants

• Connection domain is between the machine and the domain that the requirements are about (the remote domain)

• New domains

• Changes specification of machine

• Does not change requirements

Library controller

Members and candidates

Library staff

c Membership rules

Library controller

Members and candidates

Membership rules

Payroll System

Payroll forms

Output

C

C d

a

b

c

Requirements for payroll

Connection concerns

• Loss of information

• Errors

Control variants

• For each shared event,– Which domain controls type?– Which domain controls time?– Which domain controls who participates?

• Reading a file– Machine controls time and participants– Workpiece controls the value (type of event)

Control variant

Usage analyzer

ISP Softwarea

a: IS! {ISPOpen,ISPClose,ISPWrite}

Usage analyzer

Logfilesa

a: UA! {OpenLF, ReadLF} LF! {LogRecord(Read)}

Conclusions

• Most variants add a domain

• Variants have their own concerns

Particular Concerns

Problem Frames: Ch. 9

Concerns

• Questions to ask

• Crucial in understanding the problem

• Frame concerns

• Variant concerns

• Particular concerns

Particular Concerns

Concerns about a particular problem, not about a particular problem frame.

• Overrun

• Initialization

• Reliability

• Identities

• Completeness

Overrun

• A domain’s ability or inability to respond to each externally controlled event before the next event occurs.

• Occurs when there is a mismatch of speeds at a domain interface.– Machine too fast– Machine too slow

Strategies for slow machines

• Simple inhibition - the machine inhibits the shared events whenever it is not ready

• Ignoring - the machine ignores shared events whenever it is not ready

• Buffering - the machine buffers shared events whenever it is not ready, and participates later

Initialization

• Machine has initial state

• Problem has initial state– only start machine when domain is in proper

state– machine sets state of the domain– machine learns state of the domain

• Model has initial state

Reliability

• What happens when domain violates its description?

• Importance depends on– Likelihood of failure– Cost of failure

Reliability

Separate problem of normal operation from problem of reliability

• Detection

• Diagnosis

• Repair

Identities

• Identities concern is when the machine has an interface of shared phenomena with a set of individuals that – are not connected into any structure that

identifies them and– do not identify themselves.

Identities

• Add a structure that identifies individuals

• Model– must be initialized– must be maintained

Completeness

Does the machine do everything it is supposed to?

• Does a finite-state machine define what happens for every possible event?

• Does the description cover a large enough span?

Increasing Description Scope

• Widen participation– X can do Y

• What else can it do?

• Can anything else do Y?

• Complementary events– For each event, can the opposite event happen?

Particular Concerns

• Probably more

• A way to discover questions to ask

• Knowledge of experts