Move base interfaces of the domain into a boundary package (#1415)

internal/boundary/boundary.go

@@ -0,0 +1,27 @@
+// Package boundary contains global interfaces and other definitions that
+// define the Boundary domain.
+package boundary
+
+import "github.com/hashicorp/boundary/internal/db/timestamp"
+
+// An Entity is an object distinguished by its identity, rather than its
+// attributes. It can contain value objects and other entities.
+type Entity interface {
+	GetPublicId() string
+}
+
+// An Aggregate is an entity that is the root of a transactional
+// consistency boundary.
+type Aggregate interface {
+	Entity
+	GetVersion() uint32
+	GetCreateTime() *timestamp.Timestamp
+	GetUpdateTime() *timestamp.Timestamp
+}
+
+// A Resource is an aggregate with a name and description.
+type Resource interface {
+	Aggregate
+	GetName() string
+	GetDescription() string
+}