Upstream Prerequisites“Measure Twice, Cut Once”

“Blueprints”

Before construction, preparations must be made.

These preparations are custom built to the projects specific needs

The success or failure of the project is determined before the construction begins.

“Measure twice, cut once”: construction can account for up to 65% of total project cost.

Importance of Prerequisites

High quality practices = high quality software.◦Quality start: Focus on planning◦Quality middle: Focus on construction◦Quality End: Focus on testing

The goal of preparation is risk reduction.Most common project risks are poor

requirements and planning.Preparation for construction is not an exact

science.

Importance of Prerequisites

Causes of Incomplete preparation◦Developers with lack of expertise.◦“I want to code now!!!!” : Coding ASAP◦“I want to SEE code now!!”: Unsympathetic

managers Refuse, Trick, Educate, Relocate

Educate people about the development process.◦Appeal to logic◦Use Analogies◦Show the data

Importance of Prerequisites

Boss Test◦We’d Better start coding right away because

we’re going to have a lot of debugging to do.◦We haven’t planned much time for testing

because we’re not going to find many defects.◦We’ve investigated requirements and design so

much that I can’t think of and major problems we’ll run into during coding or debugging.

“What software am I working on?”

Different kinds of software projects require different balances between preparation and construction.

Projects tend to fall into development styles.◦Business Systems◦Mission-Critical Systems◦Embedded Life- Critical Systems

“What software am I working on?”

Business Systems◦Internet site, Games, Management information

systems, Payroll◦Planning is interleaved with construction◦Less quality assurance activities, done in

house.◦Informal

“What software am I working on?”

Mission –Critical Systems◦Embedded software, Software tools, Web

services◦Up- front planning and semi-formal

requirements◦Informal check-ins while coding◦Testing with a separate group. (In house always

done)

“What software am I working on?”

Embedded Life- Critical Systems◦Avionics software, Medical devices, Operating

Systems◦Formal and extensive planning, requirements,

and design◦Formal check-ins while coding◦Extensive out of house testing.◦Everything must go correctly

“What software am I working on?”

Sequential approach◦Upfront prerequisites

Requirements are stable Design is straightforward Low risk project Long term predictability High change cost.

“What software am I working on?”

Iterative approach◦As you go prerequisites

Unclear requirements Complex design Lots of risks Long term is not important Low change cost.

Adapt approaches based on your specific project.

Problem-Definition Prerequisite

“Mission Statement”Problem definition defines what the

problem is without a reference to a solution.

If it sounds like a problem it is a good problem definition.

“GGC students have a hard time managing all they have to do at the school.”

Problem-Definition Prerequisite

Problem definition lays the foundation of the programming process.

State the definition in the users language and not in computer terms.◦The best solution may not require

programming.Exception: When it deals with computers

◦Programming tools are buggy, compile times are slow, ect.

Requirements Prerequisite

Requirements describe in detail what a software system is supposed to do.

First step toward a solution.Allows the user to determine system

functionality.Minimizes changes mid project.Stable requirements don’t really happen but

must be strived for. On average a 25% change in requirements is

bound to happen.

Problem-Definition Prerequisite

How to handle requirement changes.◦Requirement checklist at the end of each

section◦Make the change cost known to everyone◦Set up a change-control procedure◦Use development approaches that can

accommodate changes.◦If all else fails: Dump the project. (Or at least

think about it)

Architecture Prerequisite

Software architecture is the high-level part of software design.

The frame that holds the detailed parts together.

A single document that defines constraints that apply system wide.

Provides guidance to programmers because it is detailed to the skills of the coders.

Problem-Definition Prerequisite

Architectural Components◦Program Organization

How many subsystems, what are the building blocks

◦Major Classes◦Data Design

Major files and tables◦Business Rules◦User Interface Design◦Input/Output

Problem-Definition Prerequisite

Architectural Components Con’t◦Resource Management◦Security◦Performance◦Scalability

Growth?◦Interoperability◦Localization◦Error Processing

Problem-Definition Prerequisite

Architectural Components Con’t◦Fault Tolerance◦Architectural Feasibility◦Overengineering◦Buy vs Build◦Reuse Decisions◦Change Strategy◦General Architectural Quality

How much time to spend on upstream prerequisites

10 to 20% of its effort and 20 to 30% of its time.

Allow time to consult the requirements and for revisions.

Treat requirements as its own project if necessary.

Smaller the project, less time necessary.

Key Points

Main goal is risk reductionEducate everyone about the development

process.Different projects means different

prerequisites. (Iterative vs Sequential)Problem definition RequirementsArchitectural design