Bryan Helmkamp

Presented by Jay Fields

• Business Natural Language (BNL) is Domain Specific Language (DSL)
• Traditional feedback loop: Business <- Developer -> QA
• With DSLs: Business stakeholders update logic

Benefits

• Managers—Improve efficiency
• Developers—Technical decisions not business decisions
• Business—Reduce time to market

(BNL == BSL) # => false

So?

• Concise or verbose?
  • Less technical users might need more verbose DSL
• Who’s the author?

“DSL” is too general

• BNL is a subset of DSL
• BNL characteristics differ from general DSL characteristics

The Difference

• Written as natural language
• Written by business people
  • Subject matter experts

Example specification

• “Award 2 points if the fare class is A, C, D, J, Z”
• account.award 2.points if [A,C,D,J,Z].include?(fare)

How?

• Use preprocessor…
• account.instance_eval removes need for account.
• Use gsub to downcase fares (to avoid them being read as constants)
• Fixnum.point does nothing. It’s syntax sugar.
• Remove the word “class”. Not needed by Ruby.
• gsub to add brackets around a list
• gsub to remove words without business meaning (i.e. “the”)

Result: Specification == Code

• Specification is code
• Specification is readable documentation

Descriptive and maintainable phrases (DAMP)

• More verbose, but verbosity makes them maintainable.
• Since the business users control the logic, it’s easier to maintain

Do not sacrifice readability for conciseness

• Staff changes
• Other people will eventually need to read it

Who is the user?

• Who are you designing for?
• Verbose phrases are not strictly necessary but help subject matter expert maintain the language

Training

• BNL has room for improvement if it requires any training to understand
• Make your language fit the requirements instead of the requirements fitting your language

Applications can be built 80% faster with DSL

• Actually, that’s bullshit.
• But… “A change that used to take 3-4 days now takes 10 minutes.”

Why not offload non-interesting parts of the application to people who actually care about the rules?

Getting it to execute

• BusinessLogic returns the rules from the DB
• eval it once when we change the method, then save it as a method
• One run eval again when rules change

Deployment?

• New workflow: Business <> Approver <> Production
• Developer not in the process
• Flag scripts as “active”, expire old scripts

Programmers: Are you out of a job?

• Absolutely not
• Still need:
  • Language workbench
  • Workflow
  • Syntax checking
  • Test environment

Syntax checking

• Very important
• Needed for subject matter experts
• Usually need contextual recommendations (i.e. “when the far” => “Did you mean ‘fare flass’?”)
• Can be done with AJAX

Commercial language workbenches

• MPS – JetBrains
  • Beta, but usable
  • Fowler has “hello world” examples
• Intentional—Not available

Another example—Employee compensation

• Verbose, but everyone can read it

When is BNL a bad choice?

• Broad, unrelated project
• Not necessary for programmers

How to decide?

• Who is the author?
• How frequently will the logic change?

How is this relevant to Ruby?

• Not required, but easier than in Java or others
• Need eval

More information

• http://bnl.jayfields.com