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 Commanded Behavior Control machine Control Domain C CD!C2 C3 Required Behavior CM!C1 Control Domain CM!C1 CD!C2

Commanded Information Answering machine Operator C B Y4 Op!E5 C2 Commanded Information Display AM!E3 RW!C1 C Real World E5

Commanded Workpiece? Weird machine Operator B B E3 Op!E5 Y4 Commanded Behavior User 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 Software a a: IS! {ISPOpen,ISPClose,ISPWrite} Usage analyzer Logfiles a 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