(The obligatory second slide)

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1 Agile MDA: Naked Objects & Together Control Center Dan Haywood Haywood Associates Ltd. (The obligatory second slide) I'm an independent consultant / developer / trainer Java, J2EE,.Net, RDBMS, OO, UML, AOP/AspectJ Expert in Together CC Author of "Better Software Faster" "In the best of all worlds, every IT professional and every business person who wants an IT system would read Better Software Faster." Ed Yourdon Expert in Naked Objects Through 2004/5, working with NO founders at the DSFA business object modelling contributing to the NO framework itself Various articles e.g. Naked Objects series, TheServerSide.com I like the ideas behind MDA just not the execution Page Haywood Associates Ltd.

2 A bit about MDA Raising the Level of Abstraction Abstraction means omitting detail Raising the level means omitting more detail Thus, cannot be dependent on that detail in particular, not dependent on platform specifics focus on the remaining important details e.g. the domain model But, need to regain missing detail to deploy provide a mapping to lower abstraction levels the mapping itself can encode best practice Page 3 A bit about MDA Mappings Refining more less abstract e.g code generators Abstracting less more abstract e.g. filtering Representing associate models from different metamodels e.g. UML class diagram & Java source code Migrating lightweight conversion e.g. if change Case tool Merging combines orthogonal models Page Haywood Associates Ltd. 2

3 A bit about MDA Two approaches to MDA Two principal approaches Elaborationist approach Translationist (executable model) approach Page 5 A bit about MDA Abstraction & Elaboration Under the elaborationist approach PIM abstracts out platform details PSM is an elaboration (i.e. fills in the detail) e.g. UML class to EJB classes +/or RDBMS tables QVT spec aims to standardize this elaboration PIM mapping PSM compiler Code PSM elaborated further to code PIM is marked up to direct the mapping process PSM or code can be edited e.g. to add in expressions of behaviour Page Haywood Associates Ltd. 3

4 A bit about MDA Abstraction & Translation Under the translationist model collection of orthogonal models each represents a single aspect for the domain, or for system concerns Domain Model System Model model translator Code Page 7 models are marked up to indicate bindings to each other bridges between the different models Resultant code is not edited all behaviour expressed in models A bit about MDA Some questions to be mulling Do models matter? does the business care about the model? are the incentives (to the business) right? how stable is the business, anyway? Is UML the right language? Is platform independence doable? Page Haywood Associates Ltd. 4

5 Naked Objects A radical approach to business systems design And also a book, an open source framework, a PhD thesis and a company Page 9 Naked Objects Yes, but what is it? An architectural pattern (among other things) Automatic visualization of behaviourally complete objects Presentation Application, Process, Task or Controller Domain object model Persistence Page Haywood Associates Ltd. 5

6 Naked Objects The Naked Objects Pattern Eliminates the use case controller layer encapsulate functionality back in the domain model Presentation (We simplify here a little for the sake of a good slide sequence ) (Behaviourally complete) Domain object model Persistence Page Naked Objects The Naked Objects Pattern Generic presentation layer reflects the domain model as an object-oriented user interface (Behaviourally complete) Domain object model Persistence Page Haywood Associates Ltd. 6

7 Naked Objects The Naked Objects Pattern Auto-generate the persistence layer for a standalone system or if prototyping (Behaviourally complete) Domain object model Page 3 Rosa's Breakfast Service The Model BreakfastOrder +actioncalculatetotal:void +actionaddbreakfast:void +createtransientinstance:b Customer Address {r} streetnumber:textstrin {r} street:textstring {r} city:textstring {r} postalcode:textstring {r} telephonenumber:texts Using TCC to visualize the "PIM" {r} total:money {rw} address:address +actioncreateorder:breakfa 0..* {r} deliverydate:date +createtransientinstance:c {r} deliverytime:time +setup:customer {r} discount:money {r} orderdate:date {r} accountnumber:wholen {r} breakfasts:internalcolle {r} breakfastorders:interna {rw} customer:customer {rw} address:address 0..* Breakfast 0..* +actionchangecomestible:v +actionchangecomestible:v +create:breakfast {r} number:wholenumber {r} changes:internalcollect {rw} standardbreakfast:sta 0..* Change Comestible +aboutbreakfast:void +createtransientinstance:c +aboutcomestible:void +setup:comestible 0..* +createtransientinstance:c 0..* {r} name:textstring {r} quantity:wholenumber {r} minimalquantity:whole {rw} breakfast:breakfast {r} price:money {rw} comestible:comestible {r} transportform:textstri StandardBreakfast +actionaddcomestible:part +createtransientinstance:s +setup:standardbreakfast +findbytitle:standardbreakf 0..* {r} name:textstring {r} parts:internalcollection {r} price:money {rw} style:style..* Part +createtransientinstance:pa {r} quantity:wholenumber {rw} standardbreakfast:sta {rw} comestible:comestible Style +createtransientinstance:s +setup:style {r} number:wholenumber {r} name:textstring Case study from MDA Explained Kleppe, Warmer & Bast (Addison-Wesley, 2003) "Breakfast in bed" for your loved one Page Haywood Associates Ltd. 7

8 Rosa's Breakfast Service The Running Application (Demo) Page 5 Page 6 Rosa's Breakfast Service The Code Application consists of domain classes only public void actioncalculatetotal() { Money price = new Money(); price.setvalue(0); // price of standard breakfast's parts for (Enumeration enum = this.breakfasts.elements(); enum.hasmoreelements();) { Breakfast breakfast = (Breakfast)enum.nextElement(); Map quantitiesbycomestible = new HashMap(); StandardBreakfast sb = breakfast.getstandardbreakfast(); if (sb!= null) { for (Enumeration enum2 = sb.getparts().elements(); enum2.hasmoreelements();) { Part part = (Part)enum2.nextElement(); if (part.getcomestible()!= null) { quantitiesbycomestible.put( part.getcomestible(), new int[] { part.getquantity().intvalue() } ); } } } // price of any changes for this breakfast // apply discount (if any) price.subtract(getdiscount()); gettotal().setvalue(price); objectchanged(); // workaround for bug in NO framework return; } 2004 Haywood Associates Ltd. 8

9 Rosa's Breakfast Service Using Together for Documentation (Demo) Page 7 Rosa's Breakfast Service executable Acceptance Tests The NO framework also has its own testing framework Allows user interactions to be scripted as JUnit tests Fixtures are shared with application itself failing tests can easily be verified Moreover at compile time, Together can create user-reviewable documents from the test source code at run time, XATs create a journal as each test passes XATs are used as the basis for: business rule definition scenario testing (UAT) Page Haywood Associates Ltd. 9

10 Rosa's Breakfast Service executable Acceptance Tests Public Sub testcancreatebreakfastorder() cust.assertactionusable( _ "Create Order", _ params(new NoDate, New NoTime, New Money)) End Sub Public Sub testcreatedefaultscustomerandparameters() Dim neworder As TestObject = _ cust.invokeaction( _ "Create Order", _ params(new NoDate(2003, 4, ), _ New NoTime(7, 45), _ New Money(20.0)) neworder.assertfieldcontains( _ "Customer", cust) neworder.assertfieldcontains( _ "Delivery Time", New NoTime(7, 45)) neworder.assertfieldcontains( _ "Delivery Date", New NoDate(2003, 4, )) neworder.assertfieldcontains( _ "Discount", New Money(20.0)) End Sub We're being agile, so let's do a quick mod Page 9 Naked Objects & Together The DRY Principle "Every piece of system knowledge should have one authoritative, unambiguous representation. Every piece of knowledge in the development of something should have a single representation. A system's knowledge is far broader than just its code. It refers to database schemas, test plans, the build system, even documentation." Dave Thomas (Pragmatic Programmer) Naked Objects & Together CC make this achievable At run time The NO pattern itself sync domain and UI XAT journal At compile time Together CC itself sync model and code Documentation generation XATs for customers BOM for developers (and I'll talk about the database next slide) Page Haywood Associates Ltd. 0

11 Naked Objects Deploy to your favourite platform Naked Objects framework is written in Java. compiles to class files, run on JVM compiles to IL, run under.net Write domain objects in your favourite language for Java/J2EE, typically just Java for.net, any of C#, VB.Net, J# Domain objects are (typically) just POJOs no compile-time dependencies on framework can define your own programming model semantics can be tested outside the framework integrate seamlessly with other POJO-based frameworks Deploy to an app server either J2EE or IIS Page 2 Naked Objects A quick peek at the Architecture PC Client Viewing Mechanism Proxy Object Manager Meta Model User Manager Container instantiates concrete instances and sets up dependencies BOM Objects Proxy Application Server Dispatcher Local Object Manager Meta Model Container User Manager Proxy Object Manager services pre- and postconditions locally, but delegates actions Local Object Manager services actions BOM Objects Transaction Manager RDBMS Object Store Container RDBMS Database Page Haywood Associates Ltd.

12 NO/TCC in the context of MDA Very definitely in the translationist camp Domain model comes to the fore represented in UML (courtesy of TCC) or in OO programming language Other aspects implemented by framework visualization, persistence & transactions, security, distribution We don't attempt platform independence you'll have to make do with either Java or.net Use Java or.net languages to specify behaviour not a new imperative language (ASL) not a declarative language (eg OCL) Page 23 NO/TCC in the context of MDA Do models matter? Only if they are exhibit immediate value to the business to the developers Does the business care about the model? yes its relationship to the running application is clear amazing connection to the domain model at high levels of management seniority Are the incentives (to the business) right? there is no expensive mapping process to debug anyway, we don't focus on reuse "a good result but a poor objective" How stable is the business? it doesn't matter: this is agile development the model is the code just focusing on the business' viewpoint Page Haywood Associates Ltd. 2

13 NO/TCC in the context of MDA Is UML the right language? No, not really. UML is very strong on static structures class diagrams in particular But is much weaker on behavioural structures state charts work to an extent proven for real-time domains, but not elsewhere interaction diagrams are instance-, not type-based OCL is declarative, not imperative ASL is a new language with no concrete syntax coupling to vendor's implementation AOP languages provides similar abstractions, except Offer clear lineage with OO languages UML profiles (or other graphical notations) not yet standardized Page 25 NO/TCC in the context of MDA Is platform independence doable? Would like to create a platform-independent representation complete in and of itself then bind it to an implementation through some mechanism or another To do so means adopting a formalism to describe that representation that is, UML and either ASL adopting mappings to elaborate / translate those models either proprietary or based on QVT investing in mappings for today's run-time platforms At best, we can be independent of run-time platform Though elaborationist approach can't really manage even this (typically that's where behaviour must be specified) but we can't be independent at development-time need to depend on tools to capture models & perform mappings Page Haywood Associates Ltd. 3

14 What to do? MDA describes a problem worth solving bind a problem domain to an implementation technology Best bet is to be pragmatic For business systems, target support both.net and Java both use a VM, so we can expect long lifetimes Use a 3GL to express behaviour Reuse a fundamental architectural style that is platform independent Use a POJO-based solution no coupling to vendor And while you're at it, employ agile principles Page 27 Summary It's all about binding the PIM to the implementation Naked Objects provides default (but pluggable) bindings for various system aspects visualization (obviously) persistence & transactions security distribution programming model semantics The combination of Naked Objects and Together CC enable the DRY principle and that in turn helps keeps things agile.net and Java support provides pragmatic platform independence Page Haywood Associates Ltd. 4

15 Agile MDA: Naked Objects & Together Control Center Dan Haywood Haywood Associates Ltd. Resources SPA2005 Conference, 0-3 April 2004 Haywood Associates Ltd. 5