About us

About your professor...

• Working for USJ part-time during the last 7 years
• Works for Telefónica R&D
• Previously Head of Engineering for FirefoxOS
• Currently CTO of the Data Transparency Lab (http://datatransparencylab.org/)
• Love Software Development, in particular anything related to how different aspects affect Software Quality
• Web Technologies are key to me: JavaScript, HTML, CSS...
• Privacy and Transparency advocate, especially because I believe Data is the next big thing
• On a personal part... 3 kids, love chess and music

About you?

• David Pérez, David Luna, Patrick Caddeo, Ioannis Strouziotis, Anastasios Plestis

• Programming Languages?
• Methodologies
• Tools: Trello, Bugzilla, Redmina, SVN, Git, etc...
• Anything else?

and...

WHY DO YOU THINK SOFTWARE QUALITY IS IMPORTANT TO SPEND THE NEXT 4 MONTHS TALKING ABOUT IT?

Content

Unit 1

Introduction to Software Quality

Unit 2

Software Quality Metrics

Unit 3

Software Configuration Managment

Unit 4

Testing

Unit 5

QA Activities beyond Testing

Methodology?

Open Discussions

PLEASE DO INTERRUPT ME FREQUENTLY

I'D PREFER TO TALK ABOUT ANYTHING THAT WORRIES YOU THAT ABOUT WHAT WORRIES ME

Practice based as much as possible

BUT

BEAR IN MIND THAT THERE IS SOME THEORETICAL AND EVEN PHILOSOPHICAL PARTS WE CAN'T AVOID

NEED TO WORK AT HOME!

NOT TO MEMORIZE BUT TO LEARN

Evaluation?

Intro

AT&T Bug

"The Jan. 1990 incident showed how bugs in self-healing software can bring down healthy systems, and the difficulty of detecting obscure load- and time-dependent defects in software."

1990: A mis-placed "break" clause in the code caused 50% of the AT&T calls fail during 9 hours ($60 million)

Software Crisis

The demand of highly skilled software developers have surpassed the offer of good development resources

Complexity of problems to be solved via software have outpaced the improvements in software development

... and having good disclaimers or lawyers is not a remedy

What is Software Quality?

What is Quality?

Easy to identify intuitively but difficult to explain, define or measure

... and highly influenced by the environment

Quality of an essay?

Usually you know which one you like the most but it's difficult to explain why

Situation determines quality?

Think about having the same meal in a nice place, with nice silvers, fantastic service or having in an awful place with plastic fork, lame service...

Would you perceive the same meal quality?

Software Quality: View1

Formal Definition

Conformance to explicitly stated functional and performance requirements, explicitly documented development standards and implicit characteristics that are expected from all professionally developed software"

1. Software Requirements
2. Specified Development Standards
3. Implicit Requirements

Can you think about examples of any of these 3 types of requirements/standards ?

- + ?

+ - ?

complexity to check conformance?

Software Quality: View2

Human point of view

Product Quality is...

Implicit requirements... there is something more beyond what is explicitly required

USERS AND THEIR EXPECTATIONS

How much it changes the world for better

or

... the value to some person

The degree it meets:

- Specified Requirements

- User needs or expectations

INFORMALLY

FORMALLY (IEEE)

Are all of you going to perceive exactly the same quality in the same product?

As engineers you should not only care about requirements.

What else you should be thinking about?

Software Quality: View3

Internal vs External Quality

Does the software do what is supposed to?

Conformance

Reliability

Accuracy

Robustness

Usability

Is the software implemented in the way it was supposed to be?

Conformance

Standards

Best Practices

But if our target is making software for end-users, should we care about internal quality?

http://blog.codinghorror.com/paying-down-your-technical-debt/

Some properties that are linked to internal quality are:

• Concision: the code just does what is supposed to be doing
• Cohesion: each module devoted to one purpose
• Low Coupling: reduce dependencies reduce error propagation
• Simplicity: Always as simple as possible so it's less error-prone
• Generality: use general solutions vs. specific ones ease maintenance
• Clarity: so it's easy to be understood and maintained

Sometimes external problems are symptoms of internal problems. This is specially true when the software is evolving and the need to change it is affected by the poor internal quality.

Software Quality: View4

ISO 9126

The Quality is determined by the Development Process, the Product itself and the usage of the Product

Software Quality: View4

ISO 9126

Does it work with the required performance for a period of time?

Does it work as expected?

Is it easy to use?

Does it  just use the required amount of resources but no more?

Is it easy to make modifications to the software?

Can it be re-used to other environments?

Are these all characteristics equally important for any product?

Summary:

Not a single definition of quality!

Quality of a product is extremely subjective and affected by the process for implementing it.

External quality is essential, but internal quality might be even more important as it affects software in the long-term and it's more difficult to be measured

Different products have different purposes, and hence, the key aspects for determining their quality should be different

KEY DEFINITIONS

KEY CONCEPTS

• Fault / Bug / Defect: Mistake in the software. I.e. something the developer did wrong.

• Error Situation / Fault: System state in which the system was not expected to be. I.e. it occurs when a buggy code is executed.

• Failure: Any deviation of the observed behaviour from the specified behaviour. I.e. something that the end-user notices.

Peter is driving his car towards Oxford. While he is driving, the road diverts into two different directions:
  1.  Left road to Oxford
  2.  Right road to Cambridge

By mistake, Peter takes the road to Cambridge. That is a fault that is committed by Peter.

Suddenly, Peter is in an error situation or state: Peter is heading 
Cambridge and not Oxford.

If Peter goes on and arrives to Cambridge, that would be a failure: 
Peter was planning to get to Oxford but he has arrived to Cambridge instead.

If Peter realizes of the error situation while he is driving Cambridge, returns to the junction and takes the right road to Oxford no failure would happen as Peter recovers from the error condition.

A REAL WORLD EXAMPLE

public static int numZero (int[] x) { 
  // effects: if x == null throw NullPointerException
  // else return the number of occurrences of 0 in x 
  int count = 0; 
  for (int i = 1; i < x.length; i ++) {
    if (x[i] == 0) { 
     count ++;
    }
  }
  return count;
}

A SOFTWARE EXAMPLE

Is there any bug?

In which circumstances will there be a failure?

Bugs

Faults

Failures

Source Code

Internal Exec Status

External Exec Status

The developer committed a mistake

... that led to a wrong situation

... which impacted the end-users

CAUSE - EFFECT

Some Examples

Therac-25

Therac-25 was a linear accelerator used in hospitals during the 80s to treat cancers. The machine had two possible configurations:

• Mode A: Radiate high energy on cells with cáncer without damaging the cells sourrounding them. There was no need to protect the patient in this mode.

• Mode B: Radiate X-rays with megavolts power that required filters and special protection to the patients.

People who operated the machine acquired great experience managing the machine and entering the command sequence to start the treatment, which they did very fast.

However, due to a programming bug, if during the process they made a sequence of operations in less than 8 seconds, the machine could use the wrong mode due to a race-condition. Because of this bug 5 people died and tens of them suffered the consequences of being exposed to a high radiation because treatment B was applied instead of mode A.

• Think about the concepts of Bug, Error Situation and Failure in this example.

• Think about some measurements that allow containing the bug in a way that the bug did not lead to a failure or at least the failure consequences were minimized.

Zune Player

SOFTWARE QUALITY ASSURANCE

SQA TARGET

Improve Software Quality

What? Reducing two things:

#1 - Number of defects

#2 - defects' impact to users

How?

It depends! an answer typical from Spotify :-) way of working

Bugs

Faults

Failures

HOW?

Devs

What can we do to reduce #defects and their impact?

Prevent
Remove
Contain

Prevent

Actions intended to minimize the number of defects that are injected in the software by developers

Can you think about ways to prevent defects?

Remove

Actions intended to remove defects once they have been injected

Can you think about ways to remove defects?

Contain

Actions intended to avoid or minimise any impact defects have on end-users

Can you think about ways to contain defects?

Bugs

Faults

Failures

Devs

Defect Prevention

Fault Tolerance

Defect Removal

SOFTWARE QUALITY ENGINEERING

 QUALITY IMPROVEMENT PROCESS

SOFTWARE QUALITY AND SOFTWARE ENGINEERING