dci - data, context and interaction @ jug lugano may 2011

DCIData, Context and

InteractionFabrizio Giudici, Senior Java Architect

Tidalwave s.a.s - [email protected]

Wednesday, May 18, 2011

DCI

About the speaker

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DCI

About the speaker

• Senior Software Architect, Mentor, Technical Writer

• Fourteen years of Java experience (JSE, JEE, JME, etc...)

• Sun partner since 1998, Oracle consultant since 2010

• Author of a number of open source projects

• Speaker at JavaOne, Devoxx, Jazoon, JAX and other events

• Member of the NetBeans Dream Team

• Co-leader of JUG Milano

• Java.Net blogger at http://www.java.net/blogs/fabriziogiudici

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DCI

Agenda

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DCI

Agenda

• A real world example

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DCI

Agenda


• DCI - Basic concepts

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DCI

Agenda



• DCI - How to implement?

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DCI

Agenda



• DCI - How to implement?

• Some simple examples

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A real world example


DCI

Shameless Plug

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DCI

Shameless Plug

• Exercises of Design - my design book...

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DCI

Shameless Plug


• Just started!

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DCI

Shameless Plug


• Just started!

• http://exercisesofdesign.java.net

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http://exercisesofdesign.java.net

http://exercisesofdesign.java.net

DCI

The Observation API

• A core component of blueBill Mobile

• An application about recording bird observations

• Designed with a high degree of abstraction

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DCI 7


DCI

The Taxonomy API

• Models the taxonomy of a philogenetic tree

• The standard way of biology for representing (bird) species

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DCI 9


DCI

So, what about a Bird?

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DCI


• Both a Taxon and an Observable

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DCI



• Multiple inheritance?

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DCI




• Multiple interface implementation?

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DCI





• Composition

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DCI





• Composition

• Taxon and Observable are roles

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DCI





• Composition

• Taxon and Observable are roles

• A Bird, in some contexts, could be a Taxon and/or an Observable

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DCI - Basic Concepts


DCI

Data, Context and Interaction

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DCI


• OOD best practice formalized by Trygve Reenskaug

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DCI



• The formalizer of MVC

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DCI




• Seen by somebody as an evolution of MVC

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DCI





• But it doesn’t replace it

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DCI






• It rather broadens the analysis scope

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DCI






• It rather broadens the analysis scope

• http://www.artima.com/articles/dci_vision.html

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DCI

DCI - aims

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DCI

DCI - aims

• Improve readability of a OO system

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DCI

DCI - aims


• Give system behaviour first-class status

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DCI

DCI - aims



• Recover readability of system properties on the whole

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DCI

DCI - aims




• Separate responsibilities for behaviour and domain

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DCI

DCI - aims





• Behaviour: what the system does

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DCI

DCI - aims






• Domain: what the system is

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DCI

DCI - aims






• Domain: what the system is

• Be close to people’s mental model

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DCI

DCI - Data

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DCI

DCI - Data

• What the system is

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DCI

DCI - Data


• Relatively static with relations

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DCI

DCI - Data



• Domain structure implemented with “conventional” classes

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DCI

DCI - Data




• Hmm... perhaps anemic classes?

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DCI

DCI - Data





• Typically it includes persistence

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DCI

DCI - Data






• Comes from the mental model of system stakeholders

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DCI

DCI - Data







• Close to the “model” in MVC

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DCI

DCI - Data







• Close to the “model” in MVC

• E.g.: BankAccount with increase(), decrease(); no deposit()

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DCI

DCI - Context (and Roles)

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DCI


• Associated to a use case, user story, scenario, or algorithm

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DCI



• Identifies objects participating in a scenario

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DCI




• Assign to each object one or more stateless roles

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DCI





• Objects can have multiple roles at the same time

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DCI






• Decompose the scenario into roles, not objects

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DCI







• Contrast this with polymorphism and classic OO decomposition

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DCI







• Contrast this with polymorphism and classic OO decomposition

• E.g.: MoneyTransfer.{.withDraw(),.deposit()} with srcAccount and destAccount

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DCI

Quick terminology note

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DCI


• Methodless role: abstract role

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DCI



• Interface, abstract class

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DCI




• Methodful role: concrete role

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DCI




• Methodful role: concrete role

• Concrete class

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DCI

DCI - Interaction

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DCI

DCI - Interaction

• What the system does

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DCI

DCI - Interaction


• Occurs among roles, which act as adapters among objects

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DCI

DCI - Interaction



• Roles are bound in different ways for each context

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DCI

DCI - Interaction




• Roles life cycle is likely to be bound to a given interaction

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DCI

DCI - Interaction





• Roles should be generic

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DCI

DCI - Interaction






• Interaction should be explicit given roles nature

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DCI

DCI - Interaction






• Interaction should be explicit given roles nature

• Hmm.... rather than emergent as in agile design?

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DCI

DCI - Execution Model

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DCI


• The Context finds object participants

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DCI



• Then, it assigns (injects?) roles to them

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DCI




• Roles are discovered by type (methodless roles)

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DCI





• Then, it triggers a method on the first role

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DCI





• Then, it triggers a method on the first role

• Interaction goes on among other roles until the job is done

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DCI

Some issues

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DCI

Some issues

• What about anemic objects?

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DCI

Some issues


• Perhaps not a problem considering clusters object + roles

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DCI

Some issues



• Object schizophrenia

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DCI

Some issues




• Which is the identity of an object in a cluster?

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DCI

Some issues





• What about equals() / hashcode()? Are roles parts of identity?

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DCI

Some issues






• Possible solution is an Identifiable role

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DCI

Some issues







• Injected by context

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DCI

Some issues







• Injected by context

• Objects with the same identity are “equals”

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DCI - How to implement?


DCI

Implementation issues

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DCI


• Static vs dynamic

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DCI



• Java

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DCI



• Java

• AOP, annotation-driven code generation (e.g. Qi4J)

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DCI



• Java


• Other languages

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DCI



• Java


• Other languages

• Traits, mix-ins

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DCI



• Java


• Other languages

• Traits, mix-ins

• First, acknowledge that DCI is a best practice

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DCI



• Java


• Other languages

• Traits, mix-ins


• Some languages can fit better than others

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DCI



• Java


• Other languages

• Traits, mix-ins



• Frameworks might help... but they force a new nature

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DCI



• Java


• Other languages

• Traits, mix-ins



• Frameworks might help... but they force a new nature

• My point: DCI must be addressed in design

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DCI

Abstracting and sweetening

• Would be nice to be technology independent

• Would be nice to have some syntactic sugar

• Note: not central in this presentation, but needed for code examples

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DCI

NetBeans Platform Lookup; as()

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DCI


• Role role = object.getLookup().lookup(Role.class) ...

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DCI



• NetBeans Platform’s Lookup, as a bag of roles

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DCI




• Allows both static implementation and dynamic injection

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DCI





• Role role = object.as(Role);

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DCI





• Role role = object.as(Role);

• My syntactic sugar around Lookup

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Some examples


DCI

Some example reusable roles

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DCI


• Displayable:

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DCI


• Displayable:

• String s = myObject.as(Displayable).getDisplayName();

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DCI


• Displayable:


• IconProvider:

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DCI


• Displayable:


• IconProvider:

• Icon i = myObject.as(IconProvider).getIcon(16);

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DCI


• Displayable:


• IconProvider:


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“ask” approach


DCI


• Displayable:


• IconProvider:


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“ask” approach

“tell” approach


DCI


• Displayable:


• IconProvider:


• Renderable:

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“ask” approach

“tell” approach


DCI


• Displayable:


• IconProvider:


• Renderable:

• PrintWriter pw = ... //myObject.as(TextRenderable).render(pw);

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“ask” approach

“tell” approach


DCI


• Displayable:


• IconProvider:


• Renderable:


• JLabel label = ... // from SwingmyObject.as(JLabelRenderable).render(label);

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“ask” approach

“tell” approach


DCI


• Displayable:


• IconProvider:


• Renderable:



• TextView textView = ... // from SwingmyObject.as(TextViewRenderable).render(textView);

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“ask” approach

“tell” approach


DCI


• Displayable:


• IconProvider:


• Renderable:



• TextView textView = ... // from SwingmyObject.as(TextViewRenderable).render(textView);

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“ask” approach

“tell” approach

Roles can be dynamically injected,so myObject does not depend on them


DCI

Examples from blueBill

• ObservationSet set = ... ;set.as(ObservationSetTraverser) .visit(new KMLReportGenerator()); // visitor pattern

• ObservationItem item = ...;TextView textView = ...;item.as(Taxon) .as(TextViewRenderable) .render(textView);

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DCI

Example: decorating roles

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DCI

Q & A

• Question Time

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dci - data, context and interaction @ jug lugano may 2011

Technology