Life above the service tier preso v1 0

Life above the Service TierHow to Build Application Frontends in a ServiceOriented World

Ganesh PrasadRajat TanejaVikrant Todankar

October 2007

Illustration: “Three Worlds”,M.C.Escher, 1955 Lithograph

All M.C. Escher works © 2007 The M.C. Escher Company the Netherlands. All rights reserved. Used by permission. www.mcescher.com

© Copyright Ganesh Prasad, Rajat Taneja, Vikrant Todankar, 2007This work is licensed under a Creative Commons AttributionNo Derivative Works 2.0 License.

http://www.mcescher.com/

Life above the Service Tier 2

Who Are We?

Ganesh PrasadSenior Architect, Westpac Banking Corporation

Rajat TanejaChief Architect, Zurich Financial Services Australia

Vikrant TodankarSenior Consultant, Hyro Limited (formerly with EDS)


Life in the Business Logic Tier is Moving Along SOAmmingly...

...but the Presentation Tier is a mess.

SOA principles - Loosely coupled systems, no implicit dependencies, all legitimate dependencies in the form of explicit contracts.

No such architectural blueprint exists for the Presentation Tier.

Two Service Models today:

SOAP-based Web Services REST

Both are based on XML document exchange.

Any Presentation Tier technology should be able to interface to legacy services painlessly, i.e., should support both SOAP and REST.


The Presentation Tier and its Three Main Processes

ClientApplication

Network

Business Logic

(Service)

Download Server

PersistenceApplicationContainer

Application Download

ClientApplication

Network

Business Logic

(Service)

Download Server


Presentation Flow

ClientApplication

Network

Business Logic

(Service)

Download Server

Persistence

ApplicationContainer Data Interchange

Service Interface



ClientApplication

Network

Business Logic

(Service)

Download Server



ClientApplication

Network

Business Logic

(Service)

Download Server


Presentation Flow

ClientApplication

Network

Business Logic

(Service)

Download Server

Persistence


Service Interface



ClientApplication

Network

Business Logic

(Service)

Download Server



ClientApplication

Network

Business Logic

(Service)

Download Server


Presentation Flow

ClientApplication

Network

Business Logic

(Service)

Download Server

Persistence


Service Interface



ClientApplication

Network

Business Logic

(Service)

Download Server



ClientApplication

Network

Business Logic

(Service)

Download Server


Presentation Flow

ClientApplication

Network

Business Logic

(Service)

Download Server

Persistence


Service Interface



ClientApplication

Network

Business Logic

(Service)

Download Server



ClientApplication

Network

Business Logic

(Service)

Download Server


Presentation Flow

ClientApplication

Network

Business Logic

(Service)

Download Server

Persistence


Service Interface

With Thin Clients, the Web Server plays a role in all three processes.


However...

The Thin Client Model has Three Flaws


Flaw 1 – Lack of Respect for Data

Name “Joe Bloggs”

BirthDate “01-JUL-1978”

AnnualSalary “120000.00”

NoOfDependents “3”

From Browser to Web Server

From Web Server to Browser

<Presentation-Markup>Data</Presentation-Markup>

Data Structures

Flattened to a set of Name-Value pairs

Data Types

Everything reduced to a String

Data Constraints

None

Data as Data?

Specialised formatting and markup for

Presentation

We can do better than this!


Flaw 2 – Coupling of Presentation Flow and Data Interchange

Server

Client

GET GETPOST

Page 1

Page 2

Page 3

Page 1 Page 2 Page 3

What the user wants to do (Presentation Flow)

What the browser does in response (Data Interchange)

GET GETPOST

Symptom – Remember the Browser Back-Button Problem?

Unsafe operation!

Yes, the POST-Redirect-GET pattern fixes this problem, but the fundamental architecture is broken.


Flaw 3 – No Support for Peer-to-Peer Data Interchange

ClientApplication

NetworkBusiness

Logic(Service)

Web Server PersistenceApplicationContainer

Client/Server (Request/Response)

Server messages can only be in response to client

requests – no unsolicited messages such as event

notifications


AJAX is the Answer!NOT!

AJAX provides Raw Capability, not Architecture.

We can build badly architected applications even with AJAX.

Thin Client(Browser) Network

Business Logic(Service)

Web Server

Persistence

Service Interface

Application DownloadPresentation FlowData Interchange

Data Interchange

AJAX Data Interchange

Web Server drives Presentation Flow

based on Data Interchange requests

Web Server acts as intermediary for Data

Interchange

Data is still treated shabbily

So what is the answer?


The Answer

...is an architecture that decouples orthogonal concerns and respects data.


So What Technologies Can We Use?

The following technologies and frameworks are available today:

DHTML/AJAX frameworks for Current Browsers 1. Handcrafted DHTML/AJAX with Third-Party JavaScript Libraries 2. Google Web Toolkit (GWT, GWT-Ext) 3. TIBCO General Interface Builder

XML Dialects for Advanced Browsers 4. XForms embedded in XHTML 2 5. Mozilla XUL 6. Microsoft SilverLight/XAML

Java-based Technologies 7. Java WebStart (Swing, SWT, Spring Rich Client) 8. JavaFX

Adobe Flash Runtime-based frameworks 9. Adobe Flex10. OpenLazslo

The degree of fit with the SOFEA model varies, but designers play a critical role in ensuring compliance with the model. We also need to consider factors like performance, ease of use, etc.


What Is Our Contribution?

A cleaner architectural model for the Presentation Tier that decouples the orthogonal concerns of Application Download, Presentation Flow and Data Interchange. Positioning the web server as a Download Server alone. The evils of web server involvement in Presentation Flow and Data Interchange are avoided. Affirmation of MVC rather than Front Controller as the natural pattern to control Presentation Flow. End-to-end data integrity in Data Interchange, which traditional thin-client technology does not and cannot enforce. Unification of the thin-client and rich-client models, now seen as an artificial distinction. Support for SOAP- and REST-based business services, and a natural integration point between the Presentation and Service Tiers


Thanks!

Technology

Life above the service tier preso v1 0