biz rules ] DB

What are Business rules? They are set by the business. These guys have written rules. Don’t ask me exactly what qualify and what don’t qualify as business rules. Business rules can be implemented in java, javascript or batch.

Many business rules are best implemented inside the DB. Reason? The concept of biz rule is popularized and heavily influenced by DB industry, vendors and practitioners. Most things that /pass as/ biz rules are defined in terms of DB records (real world objects represented by records). As a result, these biz rules can be and often are best described, saved, encoded in a DB format.

Below are just a few buzzwords, not meant to be an orthogonal, mutually exclusive list of things.

– unique constraint — eg: member id must be unique
– not-null — eg: “We can’t leave this field blank”
– RI — May not be a rule set by business, but closely related to other business rules. eg: “When this salesperson resigns, all her customers must be assigned a replacement salesperson.”
– check constraint — Can be complex. I think (??? confirmed) they should be applied at modification time.
– triggers — can implement RI, check constraints,
– – > input-validation trigger is an important, well-defined type of
– derived data — insert or update “derived data” via triggers, to let java classes select them without “deriving”. The derivation formula contain business rules.
– authorization and access control via views and stored-procs. May not qualify as business rules.
– stored proc — most flexible. Can implement the most complex rules set by business, involving multiple objects.
– – > multi-table correlated modification via stored programs
– cascade delete
– views — can contain business rules in the view’s definition query. eg: “These class of users can only read/modify this subset of data — not those protected columns or irrelevant rows. They should always see the details of each purchase — by a table join.”

An architect should learn this list of techniques. Move business rules from java classes into DB whenever possible, to reduce the complexity of java classes. A large system usually has 60-90% of the business logic implemented in application source code (like java). That’s too much to manage. It’s good to move some to javascript or DB.

[[ pl/sql for dummies ]] advocates putting most “business logic” in DB rather than java. The most complex business logic would need big guns like
* procedures
* functions
* triggers
* complex views, perhaps containing functions in their definitions and have instead-of triggers defined on them.

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