ArchiMate relationships
Eleven lines, an ordering from strongest to weakest, and a derivation rule that lets a tool answer questions you never drew. The elements are the vocabulary; this is the grammar.
11 min readArchiMate 43 of 4
01The eleven
ArchiMate has a closed set of relationships and no mechanism for inventing more. That constraint is the source of most of its value: any two people reading the same model are reading the same eleven meanings, and a tool can reason over them.
| Element | Notation | What it means |
|---|---|---|
| Composition | The whole is made of the part, and the part belongs to exactly one whole. Filled diamond on the whole. | |
| Aggregation | The whole groups the part, and the part can be grouped elsewhere too. Hollow diamond on the whole. | |
| Assignment | Active structure performs behaviour, or a node hosts an artifact. Ball on the performer. | |
| Realization | The source makes the more abstract target concrete. Points at the abstraction, always. | |
| Serving | The source provides functionality the target uses. Points at the consumer. | |
| Access | Behaviour reads, writes, or both, on a passive element. Label it read / write when it matters. | |
| Influence | The source affects a motivation element. The only relationship allowed to be vague, and the only one that can carry a sign. | |
| Triggering | Temporal order: the source completes, then the target starts. | |
| Flow | Something is transferred - information, goods, money. Label it with what moves. | |
| Specialization | The source is a particular kind of the target. Both ends must be the same element type. | |
| Association | A relationship none of the other ten describes. Correct occasionally, a smell in bulk. |
02Choosing between the ones people confuse
Four pairs account for nearly every wrong line in a real model. Each has a test that settles it in one question.
| Element | Notation | What it means |
|---|---|---|
| Serving vs realization | helps vs is | Are they the same capability at two levels of abstraction, or two different things where one is useful to the other? Same thing means realization. |
| Assignment vs realization | does vs is | A component realizes an application service; a component is assigned to an application function. Realization crosses an abstraction level, assignment crosses the structure-behaviour line. |
| Triggering vs flow | then vs carries | Triggering is about order in time. Flow is about something moving. Two steps can have both, and drawing both is fine. |
| Composition vs aggregation | one owner vs many | Could the part legitimately belong to a second whole at the same time? Yes means aggregation. |
03The strength order
The relationships are formally ordered from strongest to weakest, and the order is not trivia - it is what makes derivation work:
composition > aggregation > assignment > realization > serving > access > influence > association
"Stronger" means "makes a bigger claim". Composition says the part is inside the whole and cannot be shared; association says almost nothing. The structural relationships (the first four) are stronger than the dependency ones (serving, access, influence), which are stronger than plain association.
04Derived relationships
The rule in one sentence: a chain of relationships between two elements derives a single relationship of the weakest kind in the chain. Composition then realization then serving derives serving, because serving is the weakest of the three.
This is the mechanism that makes ArchiMate models answer questions. You draw the detailed chain once - node hosts artifact, artifact realizes component, component realizes service, service serves process, process realizes business service - and the tool can then tell you that the node serves the business service, which is the answer to "what does the customer lose if this box dies". Nobody drew that line.
The same rule explains why an over-associated model is useless. Association is the weakest relationship, so any chain containing one derives only an association - "these are connected somehow". One lazy line poisons every path through it.
05Nesting, and what it hides
ArchiMate lets you draw a relationship by putting one element inside another instead of drawing a line. It is compact and it is legal, and it is also the most common way a view becomes ambiguous: nesting can stand for composition, aggregation, assignment, realization, or specialization depending on what the elements are.
Reach for it when
- The containment is composition or aggregation and nothing else would fit
- The view is crowded and the nested elements are the detail, not the point
- Your tool records the real relationship in the model behind the drawing
- A grouping element - which is nesting used honestly, with no relationship claimed
Reach for something else when
- The relationship could plausibly be two different kinds
- The view will be exported to a picture and read without the model
- You are nesting three levels deep - draw the lines
- The nested element also has relationships to things outside the box
A safe habit: nest for composition and aggregation, draw a line for everything else. It costs a little space and removes an entire class of misreading.
06What the spec will not let you draw
Not every pair of elements can be connected by every relationship, and the constraints are worth knowing because your tool will enforce them and it is easier to agree than to fight:
- Assignment starts at active structure. A role, an actor, a component, a node. A process cannot be assigned to anything.
- Access ends at passive structure. Business object, data object, artifact, contract, material. Behaviour cannot access another behaviour.
- Influence ends at a motivation element. You cannot influence a server.
- Specialization needs matching types at both ends. An application component specializes an application component, never a node.
- Triggering and flow connect behaviour to behaviour - or active structure to active structure, when you are drawing who talks to whom rather than what happens in what order.
If the tool refuses a line, the usual cause is that one end is the wrong aspect: you meant the component and drew the service, or meant the process and drew the role. Check the aspect before assuming the rule is wrong.
In one line each
- 01Eleven relationships, closed set, no extension mechanism - that is the point.
- 02Serving points at the consumer; realization points at the abstraction.
- 03Assignment crosses structure to behaviour; realization crosses abstraction levels.
- 04A chain derives one relationship of its weakest kind.
- 05One lazy association poisons every derivation path through it.
- 06Nest for composition and aggregation; draw a line for anything else.
Related reading