add datum interface for discussion

datum_interface.go

@@ -0,0 +1,25 @@
+package meritop
+
+// Datum is the interface for basic loading and transformation.
+type Datum interface{}
+
+// DatumIerator allow one to iterate through all the datum in the set.
+type DatumIterator interface {
+	HasNext() bool
+	Next() Datum
+}
+
+// This can be used to build a sequence of Datum from source.
+type DatumIteratorBuilder interface {
+	Build(path string) DatumIterator
+}
+
+// Transform Datum from one format to another.
+type DatumTransformer interface {
+	Transform(old Datum) Datum
+}
+
+// DatumStore host a set of Datum in the memory.
+type DatumStore struct {
+	Cache []Datum
+}