Services and Complexity Roger Sessions CTO ObjectWatch.

Services and ComplexityRoger SessionsCTOObjectWatch

The Questions

Many SOAs fail.Why?What can we do about it?

The project will not meet business needs.

The project will have poor quality.

The project will be delivered late.

The project will exceed its budget.

“At-Risk” IT Projects

60% of IT budgets are invested in at-risk projects.

Costing the world economy 6.5 trillion USD per year

Costing the New Zealand economy 21 billion NZD per year

The problem is getting worse.

Exponentially!

Who cares?

What’s Causing the Problem?

Complexity!

What About ComplexityFailure rates are proportional to complexityCost is proportional to complexityAgility is inversely proportional to complexitySecurity is inversely proportional to complexity.Maintainability is inversely proportional to complexity.

The Bottom Line: Complexity is Very Bad

The Claim

Say architecture A and B both solve the business problemSay A is twice as complex as BThen A will cost twice as much, work half as well, and be twice as likely to fail as B

Example: Interlibrary Loan

Library 1

Library 2

InterLibraryLoan

Agency

Solution OneBorrower ILLA Lender

•Borrow Book•Process Positive Response•Process Negative Response

•Process Borrow Request•Request IL Loan•Process Positive Lender Response•Process Negative Lender Response•Respond to Borrower•Receive New Book Item•Update Catalog

•Process ILLA Request•Agree to Loan Request•Reject Loan Request•Process New Book

Solution TwoBorrower

ILLA

Lender

•Borrow Book•Process Positive Response•Process Negative Response•Receive Catalog

•Receive New Book Item•Update Catalog

•Process Borrow Request•Agree to Loan Request•Reject Loan Request•Process New Book

Which SOA is least complex?

- Facts and Fallacies of Software Engineering by Robert Glass

For every 25 percent increase in problem complexity, there is a 100 percent increase in solution complexity.

Glass’s Law

For every 25 percent increase in the business functionality in a service, there is a 100 percent increase in the complexity of that service.

Glass’s Law Applied to SOAs

For every 25 percent increase in the number of connections in a service, there is a 100 percent increase in the complexity of that service.

SCU = Standard Complexity Unit

The amount of complexity in an average atomic business function implemented in an idealized green field environment with no internal or external interactions.

Examples of atomic business functions:process-check, hire-employee, remove-from-inventory

1.25 functionality = 2 X complexity

Glass’s Law

Fx Cx

Bird’s Formula

A system with bf business functions is

10 log(Cx) x log(bf) / log(Fx)

times more complex than a system of 1 business function.

Bird’s Formula

is with constants replaced

Equivalent to

Simplifying Bird’s Formula

10 log(2) x log(bf) / log(1.25)

10 log(Cx) x log(bf) / log(Fx)

10 .30103 x log(bf) / .09691

Equivalent to

10 3.10 log(bf)

Glass’s Constant

A system with bf business functions and cn connections has a complexity value (in SCUs) of

10 log(Cx) x log(bf) / log(Fx) + 10 log(Cx) x log(cn) / log(Fx)

Sessions’s Formula for Service Complexity

Equivalent to

10 3.10 log(bf) + 10 3.10 log(cn)

An SOA with m services has a total complexity (in SCUs) of

Sessions’s Formula for SOA Complexity

∑i=1

m

10 3.10 log(bfi) + 10 3.10 log(cni)

Complexity of Solution OneBorrower ILLA Lender

•Borrow Book•Process Positive Response•Process Negative Response

•Process Borrow Request•Request IL Loan•Process Positive Lender Response•Process Negative Lender Response•Respond to Borrower•Receive New Book Item•Update Catalog

•Process ILLA Request•Agree to Loan Request•Reject Loan Request•Process New Book

bd comp cn comp total3 30 3 30 617 422 7 422 8443 30 4 74 105

Total: 1009

Complexity of Solution TwoBorrower

ILLA

Lender

•Borrow Book•Process Positive Response•Process Negative Response•Receive Catalog

•Receive New Book Item•Update Catalog

•Process Borrow Request•Agree to Loan Request•Reject Loan Request•Process New Book

bd comp cn comp total4 74 4 74 1482 9 2 9 174 74 4 74 148

Total: 314

Two SOA Solutions

Solution 1: 1009 SCUsSolution 2: 314 SCUsSolution 1 will cost 3 times more than Solution 2 and be 3 times more likely to fail.

But We Have a Problem

We can’t exhaustively examine every possible solution.

Why not?

For 20 business functions, there are more than 50 trillion SOA solutions.

We need a directed process.

SIP

Simple Iterative Partitions

The Process - Identification

Inter Library Loan

Borrow Loan

Ask to borrow

Process positive response

Process negative response

Receive catalog

Process request

Agree to loan

Refuse to loan

Process new book

Add book to catalog

The Process - PartitioningAsk to borrow

Process positive response

Process negative response

Receive catalog

Process loan request

Agree to loan

Refuse to loan

Process new book

Add book to catalog

A

A

A

A

B

B

B

B

C

The Process - SubsettingAsk to borrow

Process positive response

Process negative response

Receive catalog

Process loan request

Agree to loan

Refuse to loan

Process new book

Add book to catalog

A

A

A

A

B

B

B

B

C

The Process - ConnectingAsk to borrow

Process positive response

Process negative response

Receive catalog

Process loan request

Agree to loan

Refuse to loan

Process new book

Add book to catalog

Goals of SIP

A process to drive the simplest possible SOA that solves a given business problemBased on mathematical models of complexity, partitioning, and set theory.Reproducible and verifiable.

Summary

IT is in a multi-trillion dollar crisis.The major cause is complexityWe must build the simplest possible SOAs.SIP is a process for finding the simplest possible SOA.

For more information

www.microsoft.com/teched

Sessions On-Demand & Community

http://microsoft.com/technet

Resources for IT Professionals

http://microsoft.com/msdn

Resources for Developers

www.microsoft.com/learning

Microsoft Certification & Training Resources

Resources

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