What are quality attributes?

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From the course by EIT Digital

Software Architecture for the Internet of Things

133 ratings

EIT Digital

Software Architecture for the Internet of Things

133 ratings

This course will teach you how to design futureproof systems that meet the requirements of IoT systems: systems that are secure, interoperable, modifiable and scalable. Moreover, you'll learn to apply best-in-class software architecture methods to help you design complex IoT and other applications. Lastly, you'll come to understand the business impact of the technical decisions that you make as an IoT system architect. You'll learn all about software architecture in the next 5 weeks! In the first week, you'll discover why having a well-designed architecture is important and which challenges you might come across while developing your architecture. By the end of the second week, you'll already be able to write your own requirements! In the third and fourth week, you will learn how to correctly write quality attributes and quality attribute scenarios for a specific case. In the last week, you'll learn to describe your own patterns and tactics and see how they're used in an Android framework.

From the lesson

Quality Attributes

Up till now, we have been talking about quality in an informal way. However, if you want to build systems that support the required qualities you will need a way to express those quality attributes and understand how you can achieve them. After this module you should be able to formulate your own quality requirements. We will also study 2 qualities that are especially relevant for Internet of Things: interoperability and modifiability.

What are quality attributes?7:35

The nature of quality attributes4:52

Meet the Instructors

Frank Gielen
Professor
UGent/IBCN: Internet Based Communication Networks

[MUSIC]

So up till now, we have been talking about quality in an informal way.

However, if you want to build systems that support the required qualities,

you will need a way to express those qualities, and

you need to understand how you can achieve them.

After this module, you should be able to understand quality attributes and

formulate your own quality requirements.

We will also study two qualities that are especially relevant for

the Internet of things, interoperability and modifiability.

Now, quality attributes have been around for a long time,

and many of them have their own research community and interest groups.

Performance engineering, usability, and security,

all examples of such specialized communities.

The list is endless, but there are many problems with this

older approach to system quality attributes.

In many cases, the system quality is considered without any

relation to the other qualities, and each community has its own vocabulary.

Responsiveness has a different meaning for

a performance engineer than for a usability expert.

Another problem is the fact that some definitions are vague or ambiguous.

What does it mean if a system is modifiable or fast?

How can I test a requirement that states that

the system needs to have high level of usability?

Let's take the example of a mobile phone application for

looking up train schedules.

This sounds like a very simple, functional application,

the only thing we need to do is to look up something in a database.

However, users expect that such applications

have a very high level of usability.

Now, our intuition tells us that it can be somehow related to the fact that we want

to get to the train schedule of the next train with a minimum number of keystrokes.

But a usability requirement expressed as the departure station should

be available with a minimum number of keystrokes is not specific enough

to reason about the impact on the system architecture.

What does that mean, minimum number of keystrokes?

Or how do I even test this?

So it makes more sense to formulate that the mobile application

should protect the user against wrong data entries.

This is called user error protection.

And autocompletion on input fields is a way to achieve this.

Now, the autocompletion can be made context aware and

even propose a list of train stations that take into account the user location,

the actual time of the day, and previous searches.

So by now you should be convinced that usability has a big impact on

the software architecture.

And if not, you should start reasoning like a software architect and

ask yourself, what are the structures needed to

implement autocompletion in this very specific case?

Where do I get the list of available train stations?

Where do I store these lists?

How can I filter the stations close to my actual position?

Or how can I order this list in a way that the most recent searches appear first?

The usability requirement for this use case should be

rewritten as follows, a mobile user wants to look up the train

schedules using the mobile app of the railway operator.

The user interface system of the app will present a precalculated lists of departure

stations taking into account location, time, and previous search results.

The user interface of the system will also preset the departure time and

a list of three possible destinations, again, based on previous searches.

And this task will complete within three seconds after

starting the application under normal runtime conditions.

Now, this is a description of a quality attribute that already

can be tested and measured.

It can also be used to verify with the users and

customers if the specification meets the expected functionality and quality levels.

So the mobile application example allows

us now to make a more formal definition of a quality attribute.

A quality attribute, or a QA, is a measurable or

testable property of a system that is used to indicate how well

the system satisfies the needs of its stakeholders.

Now, this definition means that you can

easily verify if a quality attribute is well specified.

If you cannot quantify it or write a test case for it, it simply is not good enough,

and you need to reiterate until it satisfies this definition.

Now, the list of quality attributes is long and virtually unlimited because

as new complex systems are being designed, new quality attributes,

or new flavors of existing quality attributes, are being added.

And the application of the Internet of things to the healthcare sector,

with the introduction to medical devices, wireless sensors and

big data, has already introduced some new quality attributes.

For example, medical staff expect that the analysis and

the interpretation of medical data and medical images to be clinically correct.

In this case, it could mean that the diagnosis should be equivalent

to the conclusions of a reference group of health professionals.

Now, this new system quality attribute can be quantified

by the fact that there should be no more false negatives or

false positives that indicates of a diagnosis by a medical specialist.

It is a new type of requirement for diagnosis or

clinical equivalence, and it can lead to long and

expensive trials for the validation of a new digital system.

So as a software architect, you will rely on quality attribute definitions

to specify and analyze diverse sets of quality attributes of a given system.

The definition is the basis for

expressing the quality attributes in a more formal way.

And it forces you to capture complete and quantified information

that can be used to communicate and negotiate with stakeholders.

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