Cesar Lugo created ISIS-1360:
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Summary: Declarative Invariants
Key: ISIS-1360
URL: https://issues.apache.org/jira/browse/ISIS-1360
Project: Isis
Issue Type: Bug
Components: Core, Core: Objectstore: JDO
Affects Versions: 1.12.0
Reporter: Cesar Lugo
Assignee: Dan Haywood
Priority: Minor
I think that one aspect of the amplification concept Apache ISIS provides might
be to allow some degree of declarative business rules / invariants. There is an
interesting open source project (1) that allows a Java application to define
declarative business rules / invariant you might want to fork.
The difference between some other business rules engines (say RETE compliant)
is that most business rules engines focus on conditional business rules or
decision business rules only, and work outside the application scope, as an
external API returning results that you must incorporate into your code with
even more code. This one´s focus (ABL) is transactional business rules, which
work through the persistence manager (Hybernate´s JPA in this case), so you
don´t need to call any rules to be triggered, rules are automatically triggered
when you persist data. Thus, it lets you use the previous values before saving
and after saving to trigger rules (update inventory with new value of received
quantity - old value of received quantity + old value of inventory).
In summary, it provides:
• Declarative rules, like:
o InvoiceItem.amount = InvoiceItem.quantity * InvoiceItem.unitPrice * (1 +
VAT / 100)
o Invoice.amount = sum(InvoiceItem.amount) if InvoiceItem.status != “deleted”
o account balance = sum(invoice.amount) if status = “due
• Automatic sequencing of the rules. This is really great, because
instead of sequenced lines of code, you create independent rules, which you can
maintain and change completely separate from all other rules. You can even have
a rules manager and document each rule.
• Automatic execution of the rules every time you do an insert, update
or delete to any of those entity objects. Any change executes the rules
properly. If a new rule implies altering the sequence of the execution of
rules, this happens automatically and seamlessly.
• Extensibility (create your own rules). Create a new weightedAverage ()
rule.
• Documentation. You can document your rules, associate rules to topic
or groups, like use cases where they come from.
(1) http://www.automatedbusinesslogic.com/
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