diff --git a/docs/glossary/concept.md b/docs/glossary/concept.md
index 8528a2b..cf711c4 100644
--- a/docs/glossary/concept.md
+++ b/docs/glossary/concept.md
@@ -7,13 +7,25 @@ In order to simplify processing of incoming information people put labels on eve
 Concepts in our system have unique identifiers (CID).
 ## Compound Concepts
 
-Unlike simple (atomic) concepts like `apple`, compound concepts are always abstract, they can become concrete when we fill all their fields.
+Unlike simple (atomic) concepts like `Apple`, compound concepts are always abstract, they can become concrete when we fill all their fields.
 For example a concept a red apple:
 ```python
 EntityWithDescription {
 	entity=Apple,
-	description=ColorRed
+	description=RedColor
 }
 ```
 This concept is abstract, like `animal`, but unlike `animal` the idea that this concept has can be extended by supplying fields, in this case `entity` and `description`.
-Without compound concepts we would have to have atomic concepts like `RedApple`, `BlackCar`, `YellowCar`, etc in the knowledge base, but with compound concepts it's enough to create `EntityWithDescription`, `Apple`, `Car` and the colors to be able to express all the combinations of entities and descriptions.
\ No newline at end of file
+Without compound concepts we would have to have atomic concepts like `RedApple`, `BlackCar`, `YellowCar`, etc in the knowledge base, but with compound concepts it's enough to create `EntityWithDescription`, `Apple`, `Car` and the colors to be able to express all the combinations of entities and descriptions.
+
+## CID
+CID is a unique concept identified.
+It is recommended to give human readable names to the concepts, but because this ids don't have any semantic meaning it is possible to give arbitrary ids to concepts without breaking anything.
+
+CID of an atomic concept must contain only letters or digits.
+
+CID of compound concepts is defined as 
+```
+Name{field1=CID1,field2=CID2,...}
+```
+Where fields are sorted alphabetically and `Name` follows the rules for atomic CIDs.