Back to Basics Software Engineering. Slides covering my Atlantec 2015 talk

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The Process of Software Engineering
JohnLynch(jlynch2@cisco.com)
John Lynch

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Communication
Communicating
complex Ideas
Requirements
CostAll software
has a cost!
Software
Modelling
Quality
The true
definition of
software quality
Good
/Bad
Design
Tools
Use the
available tools! Testing
1. Functional &
Non Functional
2. An incredibly
comprehensive
software design
template
3. Symptoms of
a good and bad
design
4. Test every
line of code!

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Scenario - John and Dave are software engineers working together
on something complicated…
John is reviewing Dave’s code. Dave writes loads of code. John hasn’t a
notion what Dave’s code is doing but it certainly looks really clever. Its got
layers of inheritance and abstraction all over the place.
John is almost too embarrassed to ask what its doing but he plucks up the
courage to ask Dave how it works.
Dave gives John a very flowery overview about ‘polymorphism’, ‘abstraction’
and inter-connecting clouds. John is feeling inadequate.
John doesn’t have a clue how the code works but signs off on the review and
hopes there never comes a day where he has to take over Dave’s code!
John thinks Dave is very clever. Maybe he is but is this scenario good for the
company?

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Requirements / User
Stories
Our Starting Point.

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• Do I understand the requirements/user stories?
• And do I understand the associated non-functional
requirements / user stories?
• If not you may just solve the wrong problem OR
• You may just solve some of the problem (i.e.
60% of the time it works every time!)
1) What do I have to do?
• I understand the requirements; now how am I
going to build a solution to satisfy these
requirements?
2) How am I going to do it?

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SSO
CUCM
IM&P
HA
CUCM Jabber
ADGroups
Etc.
SRM PE ICSA GUI
System Feature
(Theme)
Product
(Epic)
Component
(User Story)
Etc.
XCP DB

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Software Modelling
The Complete Software Design Template

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1. Static Model
2. Dynamic Model3. Functional Model
Context Diagrams
Object Model Diagrams
Class Diagrams
API Definitions
Threading Model Diagrams
Etc.
Object Interaction Diagrams
Sequence Diagrams
State Machines Diagrams
Activity Diagrams
Etc.
Detailed Flow Charts
Documented Algorithms
Etc.

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1. Static Model
2. Dynamic Model3. Functional Model
Context Diagrams
Object Model Diagrams
Class Diagrams
API Definitions
Threading Model Diagrams
Etc.
Object Interaction Diagrams
Sequence Diagrams
State Machines Diagrams
Activity Diagrams
Etc.
Detailed Flow Charts
Documented Algorithms
Etc.
Wireframes
User Interaction Flows
Navigation Model
Localization
Design - Look and Feel (toolkits, technology etc..)
Etc.
4. GUI Model

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Software Modelling
1. The Static Model

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This server architecture view
shows the software layers
and the major external
interfaces. There are over 5
million lines of code in this
product!

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mtq_worker_
thread_func(
)
mtq_worker_
thread_func(
)
mtq_worker_
thread_func(
)
()
()mtq_worker_
thread_func(
)
Jabber MIO thread pool
JSM DB thread pool
mtq(m->user->q)
This is a queue of users mtq’s.
The JSM thread pool reads this queue,
removes an mtq; processes all the messages on that
users mtq. It then it moves on to the next mtq entry.
1) js_mapi_call_async() posts JSM
events into a users mtq to be processed in
the context of one of the JSM mtq thread
pool threads. This method can be called
from any thread (mio, JSM threads etc.)
3) swdb_checkout()
There is an mtq for each of the db threads. (currently 11 of these)
swdb_checkout() will suspend processing of the users mtq; push the
DB processing activity on to one of the generic DB mtq’s. One of the
DB threads carries out the DB action; un-suspends processing of the
users mtq and posts handle or pass to the users mtq.
mtq(dbpool generic mtq)
This is a queue of dbpool generic
mtq’s
JSM entry code runs in the
Context of the Jabber MIO threads before
eventually a call is made to
Js_mapi_call_async() to pass processing of
the event off to the JSM thread pool.
5) pass()/handle()
2)
4)
JSM mtq thread pool
XCP Router XMPP packet entry/exit point.

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Software Modelling
2. The Dynamic Model

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See next slide for this
exploded flow (layer 3) in
SRM!
Tracking SRM
state changes
Tracking
PE state
changes

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Software Modelling
3. The Functional Model

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• This flow covers the
sequence of operations
carried out for a Database
migration algorithm covering
3K lines of new code

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Software Modelling
4. The GUI Model

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• Provide the user navigation tree/model
Navigation Model
• Get quick feedback – ensure everyone is on the ‘same page’
Screen Mock-Ups
• Icons, graphics, colour schemes, fonts, font sizes, headings etc.
Look and Feel
• Chrome, IE, Firefox etc..
Browser Support (for Web based UI)
• Can UI be isolated for testing?
• Are there off the shelf tools available?
Testing Strategy
Etc.

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Design Validation

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Stage 1
Symptoms
• Good Traceability for user stories
• All Non functional user stories considered
• Easy to understand & quick ramp up for
fellow engineers
• Docs/wikis not too wordy - pictures are
clearer!
• Well defined boundaries of responsibility
for objects/modules
Stage 2
Symptoms
• Meets customers expectations!
• Reliable, robust & deterministic
• Easy to maintain
• Easy to extend
• Easy to debug
• Easy to test
• Good overall quality – low bug count!

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Unclear
Doesn’t meet the
customers expectations
or requirements!
Design lacks clarity
Dissatisfied
Customers
Boundaries of
responsibility
not well defined
Poorly Thought out !
Not obvious
how to
transition to
implementation
Difficult to
Debug/Test
Time is money!
Difficult
to
maintain
Buggy
Solution
Costs escalate
Absorbs
resources -
a
Bottomless
pit!

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• Test every line of code if possible.
Test, Test and more Test!
• Have you captured all the requirements?
• Does it look like it will work? (i.e. gut feeling)
• Is it easy to understand? i.e. can you easily and quickly get
feedback from peers?
• Is there a natural progression from this design to
implementation?
• Can I take a ‘divide and conquer approach!’ ?
• Is Iterative development/ continuous integration possible ?
• Can I get quick and continuous feedback during the dev.
Process ?
• Are there logical test & integration points? / Is it testable?
Early Checks

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• The name of the class/object, module or component
• Does the name make sense?
Class
• Define the key responsibilities for this object,
module, component
• Are they functionally grouped/ related?
• Are there too few? Too many?
Responsibilities
• Who talks to this object, module or component?
• Who does this object, module or component talk to?
Collaborators

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2) Design1) US def / Planning 3) Implementation 4) Test /Verification
Next iteration
New Feature
Quality Software = Quality User Stories + Quality Planning +
Quality Design + Quality Implementation + Quality Test/Verification
Shippable
Quality
Software!

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Conclusion
Summing it up!

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Our goal is clear. Produce software that meets the requirements, is delivered on time (on budget) and of the
highest quality.
If you can’t draw it you don’t fully understand it.
Build in your test strategy from the start. Test all your code.
It is our duty to ensure that our software is maintainable.
Be crystal clear on your intent.
Comment your code well. Comments are free! Be proud of what you write; make your code pretty and easy to
read.
If you are sitting at your computer and thinking how you are going to do things you probably missed a step (or two
or three  )
Quick feedback loops are one of the key ingredients to success. Use the tools available to you.
All software has a cost!
Quality at every step in the process = Software Quality

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Thank you for listening!