Notes on Interface

Architecture and Interfaces
Richard Veryard
September 2011
with thanks to Lawrence Wilkes of CBDI

Motivation
The architectural properties of a system of systems depends critically on how the systems are wired together.
Architects have a critical role in designing robust, flexible and efficient boundaries and interfaces and working space between sociotechnical systems and organizations.
Architects should help to eliminate negative and unproductive space between systems.
On the other hand, architects should help to realise positive space between automated systems – space in which people and organizations can engage positively with business and social requirements.

What is an interface?
Affordance
Ability to play same tune using multiple instruments.
Extensions
Electrical instruments have an additional precondition (switched on)
Exceptions
Cheap instruments have limited response (one note at a time).
Example: Keyboard
An abstract structure enabling many different musicians to communicate with many different instruments.
The output from the musician’s fingers becomes the input to the instrument.

Decoupling applications and technology through services
Lawrence Wilkes & Richard Veryard
Microsoft Architecture Journal, April 2004

Decoupling applications and technology with interfaces

SERVICE CONSUMERS
Frequent change
Device diversity
Multiple Devices
Workflow
ENTERPRISE SERVICE BUS
Transformation
Manage the integration process.
Assembly of consolidated components and aggregated services
Management feedback
Security and accesscontrol
Business Service Bus
Service Management
Process Orchestration
Adaptors and Transformation
Directory
Technical Service Bus – Messaging, J2EE, CORBA, Etc
SERVICE IMPLEMENTATIONS
Less frequent change
Server diversity
Interface diversity
Legacy
Apps
Packaged Apps
New Components
3rd Party Services
Enterprise Service Bus or Business Service Server
Source: CBDI Forum

SOUP
SOAPY SOUP
SOUPY SOAP
SOAP
Legacy systems
Legacy systems with some service interfaces
Service-based architecture with some outstanding legacy areas.
Fully compliant service-based architecture.
Progressive Decoupling of Legacy Systems
Source: CBDI Forum

SOA-based integration
8
Source: Hewlett Packard

Screen Scraper
Intended use of legacy …
… but intercepted
Customer Details
Customer Details
API
Legacy Software
Legacy Software

ETL = Extract, Transform and Load
Legacy Conversion
Data Warehousing
OLD
OLTP
extract
extract
Meta
Data
ETL
ETL
transform
transform
NEW
DW
load
load

Technology1
OrganizationA
Service
Technology2
Service
Organizational Boundary
Technology Boundary
OrganizationC
OrganizationB
Service
Application Boundary
ApplicationI
ApplicationII
Service = Points of Flexibility
Source: CBDI Forum

Articulation Points identify the best places to insert an interface
Lawrence Wilkes & Richard Veryard
Microsoft Architecture Journal, April 2004

Balancing Service Provider and Consumer Needs

What is a good interface?
For Service Consumer
Weaker Preconditions
Stronger Postconditions
More Generalized Model
For Service Provider
Stronger Preconditions?
Weaker Postconditions?
For Higher Reuse

Generalization
Weaker Data Model
Broad inclusive types
Broad time horizon
Weakly constrained relationships
optional
many
transferable
Stronger Data Model
Narrow exclusive types
Narrow time horizon
Strongly constrained relationships
mandatory
one
fixed

Ecological View of Components and Services

Seven Ecological Design Principles
17

References
Joshua Bloch, How to design a good API and why it matters (December 2005)
AsifHussain, Building E-Business Suite Interfaces using BPEL (Innowave Technology)
James Taylor, Managing Integration with eBusiness Suite using Oracle BPEL (Hewlett Packard)
Richard Veryard, Component-Based Business: Plug and Play (Springer 2001)
Richard Veryard, Component-Based Service Engineering (CBDI Journal, November 2003)
Lawrence Wilkes, SOA – Save Our Assets (CBDI Journal, November 2003)
Lawrence Wilkes & Richard Veryard , Service-Oriented Architecture: Considerations for Agile Systems (Microsoft Architecture Journal 2, April 2004)

If you were intrigued by this presentation …
… read my architecture blog
RVsoapbox.BlogSpot.com
… and follow me on Twitter
twitter.com/richardveryard
… and follow Lawrence on Twitter for good measure
twitter.com/lawrencewilkes

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Notes on Interface

by Richard Veryard on Sep 21, 2011

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