Requirements Engineering PPT 3

The Why-What-How Model / Goal Service Constraint Model

Goal: Why Needed? Service: What must it do? Constraint: How will we do it?

The 4 Variable Model

MCIO - Monitor, Control, Input, Output

Example : Cruise Control

1. Monitor: Variable observed in the environment (e.g. Vehicle Speed)

2. Controlled: Variables system can affect (e.g. Throttle Reading)

3. Input: Internal representation of M (e.g. Tire Rotation Sensor Readings)

4. Output: Internal representation of C (e.g. Actuator Readings)

NAT(m, c): describes nature, the environment of monitor and control

REQ(m, c): describes the requirement between monitor and control

IN(m, i): shows how monitor corresponds to their internal representation

OUT(m, i): shows how controlled corresponds to their internal representation

SOF(i, o): shows how input relates to the output

WRSPM Model / Reference Model

Venn Diagram

(e_h) Left - Domain & Requirements → Input

(e_v & s_v) Middle - Specification → Monitor, Controlled

(s_h) Right - Computer & Program → Output

the e and the s don’t have any shared

the e_v and e_h don’t have any shared

the s_v and the s_h don’t have any shared

D, S ⊧ R

P, M ⊧ S

What if the Domain assumptions are wrong

Then the Requirements will not be satisfied, does not satisfy logical statement

The difference between |– (soundness) and ⊨ (completeness)

Soundness means the statement just makes sense. Completeness takes it further and requires you list all parts of it. So even the Nurse in the domain

4 Worlds Model

1. Subject World - Domain, accountants, bankers, loan managers

2. User World - tellers, clients, managers

3. Developer World - analysts, specifiers, designers

4. System World

Each has their own FRs, NFRs