add DDD tactical guidance.

documents/00-Domain-Driven-Design-Tactical-tips/README.md

@@ -0,0 +1,38 @@
+# Quick Guidance for Domain Driven Design - Tactical design pattern
+
+## Classic Pattern guidance
+
+### Entity
+
+### Value Object
+
+### Factory
+
+Factory, just like the Factory pattern from GoF, way to encapsulate the complexity creation process and logic.
+
+could be used in : 
+> DomainService Factory, EntityFactory, 
+
+
+### Aggregate
+
+
+### Repository
+Per repository should serve or mapping to an Aggregate Root, not for Entity or Value Object
+
+### DomainService
+
+Per DomainService could provide an Entity or Value Object which is a member of Aggregate Root.
+That's means there shouldn't be any Entity or value object stand alone without Aggregate root.
+
+### ApplicationService
+
+### Module
+
+###
+
+## Advanced design guidance
+
+### Invariants vs validation
+Invariants — Invariants are generally business rules/enforcements/requirements that you impose to maintain the integrity of an object at any given time.
+