Management of Complexity in System Design of Large IT Solutions

Management of Complexity in System Design for Large IT-Solutions Dr. Michael Heiss Global Vice President for Knowledge, Innovation & Technology Dipl.-Ing. Stefan Huber Senior Architekt Siemens IT Solutions and Services © Siemens AG Austria 2009. All rights reserved.

Definition
Example: Networking generates complexity
Categories of Complexity
Strategies for Management of Complexity
Agenda

A pragmatic definition of complexity
We call a technical system complex (in contrast to complicated), if it is impossible to predict the behaviour of the whole system,
even if you know exactly how each of the system components behave and interact.
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Just a simple example Page x(t=0..4) = 0,8 x(t > 4) = 0,1 Delay one step y = x - x² y = 3,8x
3 very simple elements
3 simple behaviors
“ perfectly predictable ”
x y x y x y

Just a simple example Page y = x - x² y = 3,8x
Complexity is generated by interaction
Delay one step y 1 x = y 1 y 3 x = y 3 y 2 x = y 2

Just a simple example … ??? Page
Complexity is generated by interaction . The result is…
Even the best supercomputer of the world cannot predict more than 300 steps full precision limited precision Time steps Unpredictable!

A real-life software example
In a real world software system the number of elements, interactions and dependencies is far bigger than in the simple “toy” examples.
Example: Intelligent Networks service platform for telecom systems
(more than 100 customers worldwide)
Page

Where do we meet complexity? Page
Complexity of the „ problem space “: Real world phenomena to be solved by means of hardware and software
Complexity of the „ solution space “: How the problems are solved through hardware and software

Where do we meet complexity? Page
Organizational complexity Structure of organizations and teams
Process complexity How solutions are developed by the means of processes, methods, tools and technologies

Definition
Example: Networking generates complexity
Categories of Complexity
Strategies for Management of Complexity
Agenda

Requirements Engineering – a cycle of detecting and reducing complexity Page Detecting complexity (problem space) Info for the requirements engineer from various sources (requirements documents, interviews with stake holders, discussing prototypes, market studies,...)  The world is more complex than it seems to be at first sight Reducing complexity (solution space) Distilling abstractions out of multiple input, finding out which functions are really needed by a customer (and not everything that is stated as requirement)  Make the solution as simple as possible , as complex as needed

Usability Engineering – make solutions “user friendly”
Find the right balance in the complexity of the solution and avoid cognitive overload of users
Usage scenario driven requirements engineering (typical tasks are most important)
Prototyping with customer involvement
Standardization of user interfaces (“the Apple way...”)
Staging concepts of functionality (“one click shopping” vs. step by step)
Usability testing with “thinking aloud” technique
Page Usability testing Paper prototyping Source: SIS PSE Support Center Usability

Divide and conquer? Page
Old wisdom of statesmen and commanders
Classical principle for trying to reduce complexity :
Break down a problem into two or more sub-problems of a similar type, until these become simple enough to be solved directly + focussing - per definition not sufficient for complex systems
The Tower of Hanoi puzzle: A simple algorithm applied recursively Source: Wikipedia

Metrics are useful indicators of complexity Page
Complexity of requirements : Function Point Analysis
Complexity of code :
McCabe metrics (cyclomatic complexity)
Halstead metrics (static analysis)
Can be a hint showing
Maintainability
Risk of errors
Code worth being reworked or checked e.g. by a senior developer

Managing Software Complexity by Patterns Page Suboptimal Software Design
Monolithic or
Ad-hoc design
Complexity not manageable
Difficult to understand
Error-prone

Managing Software Complexity by Patterns Page Software Design Patterns
Managing complexity by providing higher level abstractions .
Reuse of engineering know-how
Patterns can be
named
taught
communicated
Proxy Facade Chain of Responsibility Composite Factory

Managing Software Complexity by Patterns Page Software Architecture Patterns Patterns at Software architecture level Design & Architecture Patterns Training in our Software Architect Curriculum * UI...User Interface Business Layer Data Layer Web / UI* Layer

Architectural Qualities and Tactics Page Page
Architectural Qualities (related to non-functional requirements)
E.g. performance, availability, maintainability
Architectural Tactics
Tactics to achieve certain architectural qualities
More than patterns, tactics provide straight-forward approach from non-functional requirements to a design solution
Several architectural tactics support managing complexity
Tactics Patterns guides selection of implements a collection of Qualities are achieved by using

Architectural Qualities and Tactics Page Page Tactics Patterns guides selection of implements a collection of Qualities are achieved by using Modifiability Localize modifications Layers Prevent rippling effects Explicit Interface Testability Manage I/O

Organizational patterns – experience based practices to act successfully in a specific context Page Source: Siemens IT Solutions and Services SDE Support Center PM

Acting with responsibilities instead of detailed process descriptions Page
Defining responsibilities as anchor point for software delopment
Performing software design via thinking in responsibilities (e.g. in distributed development)...
Provides a basis for independent, local decision making
Decouples development process
Similarity to management theory (away from Taylorism)
Techniques in software development:
CRC Cards ( Kent Beck / Ward Cunningham )
Classes – Responsibilities – Collaborations
“ Responsibility Driven Design”
Design by Contract
Precondition – Invariant - Postcondition

Safety nets in development processes Page
Reviews and inspections of intermediate results (specifications, plans, test cases, etc.)
Quality gates in company internal processes
Impact analyses – identifying the consequences of changes
Test driven development (specify test cases prior to developing code)
Process improvement (root cause analyses, project experience workshops, CMMI-assessments,...)

Safety nets in product design Page
Software Architectural Tactics exist to provide safety nets in the product: “Be prepared for the unforeseeable” ( self-healing systems , high system availability , etc.)
Examples:
Process / system monitoring software
Restart routines after error detection (“watchdogs”)
Load balancers
Redundancies, Voting
Heartbeat
Worker 1 Worker 2 Worker 3 Load balancer

Agile Software Development - the new paradigm for Software Engineering Page
Time boxing (fixed schedule and effort, functionality to be prioritized by customer – only really important functions are developed)
Iterative development with short iteration cycles (fast changes possible)
Refactoring (continuous improvement of design)
Test driven development
Pair programming
Self-organizing team, Scrum Master in supportive role
Source: Siemens IT Solutiond and Services SDE System Engineering Method SEM

Depending on the angle of view the same complexity might be easier to handle Page view v 1 view v 2 ? !
Example from Computational Intelligence : 4 different „languages“ to tell the computer what to do
Presenting the computer:
Examples (neural networks, case based reasoning)
Rules (fuzzy logic, expert systems)
Fitness function (optimization algorithms, genetic algorithms)
Commands (classical program code based on classical system modeling)
„ No free lunch“: non of them is better for all problems
Compare to
management theories (all 4)
Test driven development (first: examples)
Definition of non-functional requirements (first 3)
correlation visible v 1 v 2

Systems have increased interconnectivity
This leads to an increased complexity
Customers need high availability for mission critical IT systems
A high maturity in management of complex systems is required to deliver ultra-highly available and complex IT systems
Conclusion

Assoc. Prof. Dr. Michael Heiss Global Vice President for Knowledge, Innovation and Technology Stefan Huber , Senior Architect Dr. Benedikt Lutz , Head of Learning Network Martin Arnhof , Student
Siemens AG Österreich Siemens IT Solutions and Services Gudrunstraße 11 1100 Vienna Austria Phone +43-5-1707-46560 Fax +43-5-1707-56591 Mobile + 43-664-8855 1526 mailto: [email_address]
Thank you for your attention! Page

Management of Complexity in System Design of Large IT Solutions

by Michael Heiss on Jun 05, 2009

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Management of Complexity in System Design of Large IT Solutions — Presentation Transcript