Forces on architecture decisions (WICSA 2012)

Forces on architecture
decisions

Uwe van Heesch
Paris Avgeriou
Rich Hilliard
Dienstag, 14. August 2012 1

Creating software architecture
is making decisions

Architect
Uwe van Heesch - uwe@vanheesch.net

Creating software architecture
is making decisions

M a k e o r b u y? r n s t o us e?
h ich a rch i t e c t u r a l p a t te
W
ame wo r k f o r p e rs i s te n c e?
Wh ich f r e p l at f o r m?
Wh ic h m idd le wa r t s o r de s ig n?
S h o u ld we re u s e c om p o ne n
we us e o p e n s o u rc e SW?
Sh o u ld
h e re t o p u t c om p o ne n t C?
W

Architect

Each decision implies a choice between 2 or more
alternatives

?


These choices are driven by forces.


These choices are driven by forces.

prefer
OSS


Decisions are driven by forces.

Reliability



Reliability



Experience
Reliability



Experience Reliability



Strateg. development



Scalability





Scalability Strateg. development



prefer
OSS Reliability
Experience




Resulting force



A force is any aspect of an architectural problem
arising in the system or its environment ( operational,
development, business, organizational, political,
economic, legal, regulatory, ecological, social, etc.), to be
considered when choosing among the available decision
alternatives.


Typical forces


Typical forces

requirements


Typical forces

requirements business goals


Typical forces


constraints


Typical forces


regulations
constraints


Typical forces


laws

regulations
constraints


Typical forces


laws

standards

regulations
constraints


Typical forces


laws
principles

standards

regulations
constraints


Typical forces


laws
hw/sw interfaces
principles

standards

regulations
constraints


Typical forces


laws
hw/sw interfaces
principles

standards

previously made ADs
regulations
constraints


requirements
constraints business goals
laws standards principles
previously made ADs hw/sw interfaces
regulations


forces

requirements
constraints business goals
laws standards principles
previously made ADs hw/sw interfaces
regulations


How to model and document forces?


A framework for architecture decisions

Decision Decision
Relationship Chronology
Viewpoint Viewpoint
Decision
Detail VP
Decision
Stakeholder
Involvement VP
using the conventions from ISO/IEC/IEEE 42010


Decision
Relationship
Viewpoint


Decision
Chronology
Viewpoint



Decision Decision
Viewpoint Viewpoint
Decision
Detail VP
Decision
Stakeholder
Involvement VP



Decision Decision
Viewpoint Viewpoint
Decision
Detail VP
Decision Decision
Stakeholder Forces
Involvement VP Viewpoint


Example of a forces view

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decision state
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decision state
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impact rating

holder
cost, w
Concerns framed by the forces viewpoint be “not
related concerns, the stakeholders were identified in our pre-
vious work. hardwa
licenses
Table I
C ONCERNS OF THE DECISION FORCES VIEWPOINT
classifie
distribu
Code Concern
C3 What is the rationale for decision D? Apar
C4 What concerns Ci does decision D pertain to? betwee
C5 What forces Fj impact/influence decision D? of the
C6 What decisions Dk are influenced by force F ?
C7 What forces Fl have conflicting influences on decision D?
system:
C23 What decisions Dp or decision sub-graphs SGq can be
reused in other projects? ++:

Table II
T YPICAL STAKEHOLDERS OF THE DECISION FORCES VIEWPOINT AND
THEIR CONCERNS
+:
Stakeholder Concerns blank
Architect C3, C4, C5, C6, C7 Uwe van Heesch - uwe@vanheesch.net
Dienstag, 14. August 2012 Reviewer C3, C4, C5, C6, C7 22

C ONCERNS OF THE DECISION FORCES VIEWPOINT
classified by a legal concern (e.g
distributed).
Code Concern
C3 What is the rationale for decision D? Apart from a textual qualificatio
C4 What concerns Ci does decision D pertain to? between decision force and archite
C5 What forces Fj impact/influence decision D? of the following values, estimated
C6 What decisions Dk are influenced by force F ?
C7 What forces Fl have conflicting influences on decision D?
system:
C23 What decisions Dp or decision sub-graphs SGq can be
reused in other projects? ++: A force strongly suppor
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Requirements Engineer
?-/+7'<17.+6 C4, C6, C7
New project member
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C3
4#+#3;JE#.$)$-E# - -: A force strongly opposes
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4#+#3;JE#.$)$-E# %
% ence in functional progra
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a strong argument again %%
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The decision forces viewpoint consists of a single% model%
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as a programming langu
kind. Figure 3 depicts its metamodel, which presents the%
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conceptual elements for architecture models %%that adhere to&&
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instance, a force (could
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it. This model is part of a shared metamodel, which is used tributed under an open s
by all viewpoints of the decision documentation framework. would for instance preven
Together with well-defined correspondence rules, the shared as a search library. Neve

Validation of the forces viewpoint

• multiple case study
• 3 groups of graduating students
• working in non-academic SW projects
(2 industrial, 1 open source)
• used our decision framework to model ADs
• observed over a period of seven weeks


Research questions

RQ1: How does the forces viewpoint support
the decision making process?

RQ2: Which decision-related concerns does the
forces viewpoint support?


Data collection and analysis

• work artifacts
• weekly focus groups
• participant observation
• grounded theory for data analysis


Results
Table IV
R ESULT OF THE QUALITATIVE ANALYSIS

Code Category PrjA PrjB PrjC Concerns Res. Qu.
Cat1 Required students to think more carefully about decisions. X X X RQ1
Cat2 Triggered students to consider quality attribute requirements. X X X RQ1
Cat3 Prevents ad-hoc decisions. X X X RQ1
Cat4 Forces viewpoint will be used in other projects. X X X RQ1
Cat5 Triggered students to identify more alternatives. X X RQ1
Cat6 Good way to document decisions. X X RQ1
Cat7 Creating the forces view took a lot of time. X RQ1
Cat8 Prevents inefﬁcient discussions about decisions. X RQ1
Cat9 Created with reasonable effort. X RQ1
Cat10 Saved time in the end. X RQ1
Cat11 Support for rational decisions. X RQ1
Cat12 Forces view complements relationship view. X RQ1
Cat13 Useful for architects, designers, programmers, and new project members. X RQ1
Cat14 Support for weighing forces is missing. X RQ1
Cat15 Identifying all forces is a matter of experience. X RQ1
Cat16 Forces view and relationship view are simultaneously reﬁned. X RQ1
Cat17 Proper tool support needed. X RQ1
Cat18 Maintain overview over architectural decisions, concerns, and forces. X X X C4,C5,C6 RQ1,RQ2
Cat19 Helpful to systematically compare decision alternatives in the context of X X X C5,C6 RQ1,RQ2
forces.
Cat20 Help for estimating requirements coverage. X X C6 RQ1,RQ2
Cat21 Support for systematic trade-offs between forces. X C7 RQ1,RQ2
Cat22 Supports sharing architecture rationale. X X X C3, C23 RQ2

e important than other forces causing them to select an The students described that one column in the forces v
itecture decision alternative that had a lower rating (i.e. (see Figure 1) shows which concerns (Cat18, concern C4),
s of pluses and minuses) than the other alternatives. Al- which forces (Cat18, concern C5) are related to a decis
gh we had considered this aspect during the design of the
Dienstag, 14. August 2012
They also understood that a row in the view shows decis 27

Results

+ supports decision making process of
(inexperienced) designers
+ provides a structure for making systematic
decisions
+ documents rationale that went into decisions
+ satisﬁes the stakeholder concerns assigned to the
viewpoint

- different weights for forces needed
- identifying forces requires experience


Ongoing work

• decision-centric architecture evaluation based
on forces
• lists of domain speciﬁc forces
• different approaches to weighing forces
• different approaches to force impact ratings
• improved tool support for decision framework


Thank you for your
attention
uwe@vanheesch.net
paris@cs.rug.nl
r.hilliard@computer.org


Forces on architecture decisions (WICSA 2012)

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