Use cases and requirements

Written on 7 November 2013, 11:38am

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Functional vs non-functional requirements

Functional: describes the behavior of the system, its functionality; what the system should do
Non-functional: describes the performance characteristics of the system; how the system should be

Functional: the system must present the user an interface with the number of records in the db.
Non functional: the number of records must update in real-time.

Functional: the system must send an email when a new order is placed.
Non-functional: the emails should be sent with a latency of no greater than 10 minutes from such an activity.

Use cases

Use cases represent a practice for capturing functional requirements.

Use cases > scenarios:

A use case defines a goal-oriented set of interactions between external actors and the system under consideration.
A scenario is an instance of a use case, and represents a single path through the use case.
Use cases capture who (actor) does what (interaction) with the system, for what purpose (goal), without dealing with system internals.

Scenarios > use cases:

A scenario is a sequence of steps describing an interaction between a user and a system.
A use case is a set of scenarios tied together by a common user goal.
Martin Fowler – UML distilled

In order to engage all the stakeholders, the use cases should be:
– written in an easy to understand language
– kept short (1-2 pages max)
– have a narrative language (user stories)
– have a clear structure (Title, Goal, Actors, Assumptions, Steps, Variations, Non-functional requirements, Issues)


Random things that keep me busy

Written on 2 November 2013, 11:52pm

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HTTP 2.0: Google vs Microsoft compete for IETF specifications

HTTP 1.1 is backing up the web as we know it, but it starts to show up its age.

Google already built SPDY – a protocol that proves to be twice as fast as HTTP. Remember the OSI Model layer stack? SPDY adds a session layer atop of SSL that allows for multiple concurrent, interleaved streams over a single TCP connection. The main features of SPDY are:
– Multiplexed streams
– Request prioritization
– HTTP header compression
– Server push
– Server hint
More details about SPDY:

Microsoft came later in the game with a kinky proposal: HTTP S&M, Speed and Mobility. The HTTP Speed+Mobility proposal starts from both the Google SPDY protocol and the work the industry has done around WebSockets. Microsoft seems to be less concerned with speed, and more concern with the mobile apps and devices, as well as backwards compliance. As far as the Web sockets are concerned, they are a HTML5 feature aimed to address the request/response architecture of the web. There is an persistent connection between the client and the server and both parties can start sending data at any time.

A good comparative analysis here: S&M vs. SPDY: Microsoft and Google battle over the future of HTTP 2.0

In one-year time, IETF should come up with a proposal for the HTTP 2.0. Note to self: check back next year 🙂

What really happens when you navigate to an URL

Speaking about HTTP: A nice refresher about how the current HTTP (1.1) works:
DNS caching, CDN, ETag headers, Content-Encoding gzip, long-polling and the rest…

Review your privacy and cookies policy

Speaking about cookies, from a technical point of view, the only things you need to remember are the cookie attributes: name, value, domain, path, expires, secure, httponly. Server sets them, browser saves them and sends along with the subsequent requests. Ah, and don’t forget about session vs persistent cookies (see the ‘expires’ attributes).

Then, in the recent context of privacy and data protection, as a site owner it’s a good a idea to have a cookie audit. Not necessarily to comply with the EU’s privacy directive (the Cookie law), but because it’s good for the site owners and their users to have clearer policies and information on privacy.

The people at found 3 levels of approach:

Level 1 = a more prominent link to the privacy policy and improved information within the policy itself
Level 2 = user can selectively opt in/out of groups of cookies
Level 3 = active opt-in (the only one strictly compliant)

Next Captchas will be about recognizing objects in images

Speaking about privacy and data protection, it looks like the computers are catching up with humans. Using machine learning, a San Francisco-based company is working on a software with the goal of developing a sense of vision for the machines. By ‘sense of vision’ they mean:

– recognize letters wherever they appear,
– identify objects in photographs,
– and generally do all the stuff any kid with healthy vision can do

The first progress report says their software solves CAPTCHAs, on average 90% of the time.

Captcha’s original creator, Luis von Ahn, says: ‘An advance like this isn’t the end of CAPTCHA, although in time, CAPTCHA-breaking is likely to evolve to the point where companies will need to rely on another spambot gatekeeper. The next step is asking people to identify objects in photographs’. (

Apparently, the only thing where humans are better than computers remains identifying objects in pictures. Oh, wait: Google+ can now identify random, untagged objects in your photos, so you can search for “cat” and find photos of your cat purely by object recognition alone

UML: Generalization vs clasification

An easy one for the finish: be careful when you use a ‘is a’ relationship!
– classification – is an instance of
– generalisation – is a subtype of
Generalisation is transitive, whereas classification not.
Example inspired from UML Distilled

PS: iPad Air is awesome 🙂
ipad Air