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Designing your application - using UML techniques

When you're planning to write an application, you shouldn't just start writing code - you should think about what you're going to do and plan ahead. But how do you plan ahead? How do you ensure that you've thought of things from various angles?

UML (Unified Modeling Language) is a way of drawing (modeling) a system through a series of diagrams of different types - there are 7 basic types - and there are various software packages that can help you. But to go the whole hog and use them all on a small system is overkill, and on courses I often suggest to delegates it's far more practical to think things through and to know that you could draw the diagrams, rather than to draw them all with all the formally designated shapes and symbols. For an application I specified and started to write yesterday, I drew some example diagrams, which I'll share with you here.

The application requirement is to analyse a day's web server log files and extract information from them about the types and lengths of visits (a typically woolly or fluffy initial spec). Let's draw some diagrams ...

Use Case DiagramThe Use Case diagram. "Where does the data come from, where does it go, and who provides it / who requires the answers". Where "who" is a job role, rather than an individual's name. The application that I started to write is indicated by the red arrow - taking the log files and providing a management / decision helping report.


Object diagam - UMLThe Object diagrams. For each of the data types (objects), we're defining what they contain - what other objects, how many of them, etc. In this example, we're defining a "visit" as containing one or more "requests". Each visit will contain one "browser" object and one "ip" object.


Class diagram - Unified Modelling LanguageClass diagrams. Where data types have subclasses / other subsidiary types, you'll need to work out your inheritance tree. In this example, website access requests within a visit are divided into "request" objects which are specifically requested by a visiting user, and "require" objects which are called up within a page by a request - that's accesses for things like style sheets and embedded images.


A sequence diagram from UMLSequence diagrams. When the application (or a part of it) is run, what actually happens? In this example diagram, a browser calls up a web server via the http protocol. The server application may call up an SQL database, or it may use data it already has (cached?) on the local disc and not use the database stage. This diagram helps you spot bottlenecks, and provides you with a route to finding what's happened if the application fails to run to completion.


Unified Modelling Language - Deployment diagramThe Deployment diagram. This shows you all the tools that you need, how you go from test and development system through to pre-production systems, the live system, and on to backups. It will include things like the source code control system that you use, and provide you with an indication of how you can roll back if something goes wrong, and an assurance that (if you follow the diagrams) that you really do have a backup of everything so that you can roll back.


UML - State DiagramState diagrams. For each type of object - what creates it, and what happens when it's finished with. And what happens in between. If calculations are done, is that as the object is set up, or as the results are needed? Are results cached? ... for more complex objects (such as sessions in a shopping cart), what's the page the object owner - shopper - is currently on?


UML - Procedural DiagramProcedural diagrams. Also known as "flow charts" ;-) ... a diagram of the operation of each method. Procedural diagrams can be converted to actual code on some of the more sophisticated UML tools.


When you're learning Object Oriented Programming, you really need to learn the syntax and principles of the language elements, and also how to design to make best use of those elements. These diagrams - informally or formally - provide you help with the design.

There's a code example - a first (and incomplete) example showing code to support some of the diagrams above [here] from yesterday's Object Oriented Programming in PHP course.
(written 2012-02-11, updated 2012-02-25)

 
Associated topics are indexed as below, or enter http://melksh.am/nnnn for individual articles
H108 - Objects in PHP
  [4628] Associative objects - one object within another. - (2016-01-20)
  [4627] Caching results in an object for efficiency - avoiding re-calculation - (2016-01-20)
  [4626] Singleton design pattern - examples and uses - (2016-01-20)
  [4366] Changing what operators do on objects - a comparison across different programming languages - (2014-12-26)
  [4356] Object factories in C++, Python, PHP and Perl - (2014-12-19)
  [4073] Learning about Object Orientation in PHP - a new set of examples - (2013-04-28)
  [4057] stdClass in PHP - using an object rather than an associative array - (2013-04-02)
  [3953] Objects in PHP - Revision - (2012-12-16)
  [3843] Caching Design Patterns - (2012-08-20)
  [3841] Copying, duplicating, cloning an object in PHP - (2012-08-18)
  [3840] Autoload in PHP - (2012-08-17)
  [3609] How do classes relate to each other? Associated Classes - (2012-02-12)
  [3608] Design Patterns - what are they? Why use them? - (2012-02-12)
  [3211] Computer Graphics in PHP - World (incoming data) to Pixel (screen) conversion - (2011-03-24)
  [3210] Catchable fatal error in PHP ... How to catch, and alternative solutions such as JSON - (2011-03-22)
  [3142] Private and Public - and things between - (2011-01-22)
  [2922] Getting the OO design write - with PHP a example - (2010-08-14)
  [2921] Does copying a variable duplicate the contents? - (2010-08-14)
  [2774] PHP - Object Oriented Design in use - (2010-05-21)
  [2741] What is a factory? - (2010-04-26)
  [2717] The Multiple Inheritance Conundrum, interfaces and mixins - (2010-04-11)
  [2680] Static class members in PHP - a documented example - (2010-03-16)
  [2641] Object Oriented Programming in PHP - (2010-02-19)
  [2632] Shipping a test harness with your class in PHP - (2010-02-12)
  [2435] Serialization - storing and reloading objects - (2009-10-04)
  [2434] Abstract classes, Interfaces, PHP and Java - (2009-10-03)
  [2380] Object Oriented programming - a practical design example - (2009-08-27)
  [2172] PHP4 v PHP5 - Object Model Difference - (2009-05-11)
  [2171] Cleaning up redundant objects - (2009-05-11)
  [2169] When should I use OO techniques? - (2009-05-11)
  [2160] PHP - getclass v instanceof - (2009-05-07)
  [1925] Introduction to Object Oriented Programming - (2008-12-06)
  [1820] Sorting objects in PHP - (2008-10-04)
  [1819] Calling base class constructors - (2008-10-03)
  [1682] Accounts in PHP - an OO demo - (2008-06-19)
  [1535] OO PHP demonstration - comparing objects and more - (2008-02-08)
  [1217] What are factory and singleton classes? - (2007-06-04)
  [1153] Object Oriented Model - a summary of changes from PHP4 to PHP5 - (2007-04-18)
  [1027] Cue the music, I'm happy. - (2007-01-09)
  [836] Build on what you already have with OO - (2006-08-17)
  [720] Planning a hotel refurb - an example of a Gant chart in PHP - (2006-05-14)
  [656] Think about your design even if you don't use full UML - (2006-03-24)
  [485] North, Norther and Northest - PHP 5 Objects - (2005-11-04)
  [421] Don't repeat code - use loops or functions - (2005-08-21)
  [343] Should I use structured or object oriented? - (2005-06-10)
  [205] PHP5 lets you say no - (2005-02-07)
  [124] PHP v Java - (2004-11-20)
  [67] Object Oriented Programming in PHP - (2004-09-29)

Q907 - Object Orientation and General technical topics - Object Orientation: Design Techniques
  [4449] Spike solution, refactoring into encapsulated object methods - good design practise - (2015-03-05)
  [4430] The spirit of Java - delegating to classes - (2015-02-18)
  [4374] Test driven development, and class design, from first principles (using C++) - (2014-12-30)
  [4098] Using object orientation for non-physical objects - (2013-05-22)
  [3978] Teaching OO - how to avoid lots of window switching early on - (2013-01-17)
  [3928] Storing your intermediate data - what format should you you choose? - (2012-11-20)
  [3887] Inheritance, Composition and Associated objects - when to use which - Python example - (2012-10-10)
  [3878] From Structured to Object Oriented Programming. - (2012-10-02)
  [3844] Rooms ready for guests - each time, every time, thanks to good system design - (2012-08-20)
  [3798] When you should use Object Orientation even in a short program - Python example - (2012-07-06)
  [3763] Spike solutions and refactoring - a Python example - (2012-06-13)
  [3760] Why you should use objects even for short data manipulation programs in Ruby - (2012-06-10)
  [3454] Your PHP website - how to factor and refactor to reduce growing pains - (2011-09-24)
  [3260] Ruby - a training example that puts many language elements together to demonstrate the whole - (2011-04-23)
  [3085] Object Oriented Programming for Structured Programmers - conversion training - (2010-12-14)
  [3063] Comments in and on Perl - a case for extreme OO programming - (2010-11-21)
  [2977] What is a factory method and why use one? - Example in Ruby - (2010-09-30)
  [2953] Turning an exercise into the real thing with extreme programming - (2010-09-11)
  [2889] Should Python classes each be in their own file? - (2010-07-27)
  [2878] Program for reliability and efficiency - do not duplicate, but rather share and re-use - (2010-07-19)
  [2865] Relationships between Java classes - inheritance, packaging and others - (2010-07-10)
  [2785] The Light bulb moment when people see how Object Orientation works in real use - (2010-05-28)
  [2747] Containment, Associative Objects, Inheritance, packages and modules - (2010-04-30)
  [2523] Plan your application before you start - (2009-12-02)
  [2501] Simples - (2009-11-12)
  [2327] Planning! - (2009-08-08)
  [2170] Designing a heirarcy of classes - getting inheritance right - (2009-05-11)
  [1538] Teaching Object Oriented Java with Students and Ice Cream - (2008-02-12)
  [1528] Object Oriented Tcl - (2008-02-02)
  [1435] Object Oriented Programming in Perl - Course - (2007-11-18)
  [1224] Object Relation Mapping (ORM) - (2007-06-09)
  [1047] Maintainable code - some positive advice - (2007-01-21)
  [831] Comparison of Object Oriented Philosophy - Python, Java, C++, Perl - (2006-08-13)
  [747] The Fag Packet Design Methodology - (2006-06-06)
  [534] Design - one name, one action - (2005-12-19)
  [507] Introduction to Object Oriented Programming - (2005-11-27)
  [236] Tapping in on resources - (2005-03-05)
  [80] OO - real benefits - (2004-10-09)


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