Property:Scalability

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		Scalability	Version:	1.0
	Document type:	Quality Attribute	Owner:	J.A.H. Schoonderbeek

The scalability of a facility, denoted as a single string, determines how easy or difficult it will be to alter its capacity. There are two strategies available to promote scalability, namely facilitating the possibility of either internal or external scaling.

• Internal scalability is achieved by the expandability (or reduction) of individual components making up the solution (Scaling Up or Down); an example would be the addition of extra RAM in a server.
• External scalability is achieved by using more (or less) components in parallel (Scaling Out or In); an example would be the addition of extra web servers behind a load balancer.

When determining the scalability of a solution, it is advisable to devote extra attention to interfaces and aggregation points, because this is where most bottlenecks and integration issues will occur.

Defined values for Scalability:

ordinal	value	meaning
0	NS	no scalability specified
1	fixed	Capacity cannot be scaled
10	up	Capacity can be Scaled Up
15	up and down	Capacity can be scaled both up and down
20	out	Capacity can be scaled outward only.
25	out and back	Capacity can be scaled out, but also back
30	up and out	Capacity can be scaled both upward and outward
40	up, down, out and back	Capacity can be scaled up, down, in and out