A User-Oriented Model-Driven Requirements
Elicitation Process based on User Modeling
Han Liu
12
, Chao Li
1
, Jizhe Wang
1
, Qing Wang
1
, Mingshu Li
1
1
Itechs. Lab, Institute of Software, Chinese Academy of Sciences Beijing, 100080, China P.R
2
Department of Computer Science, University of Toronto Toronto, M5S 3G4, Canada.
Abstract As software is becoming more and more interweaved with people,
organizations, and social systems, the users we face are becoming more and
more complex in all aspects. On the other hand, user participation is largely
ignored in traditional requirements elicitation methods (including
Model-Driven Requirements Elicitation (MDRE) methods). In this paper, we
adopt user modeling techniques into requirements elicitation, specifically
MDRE, enhancing MDRE process into a user-oriented one, and at the same
time personalizing the requirements reuse pattern of MDRE. Our approach
facilitates user collaboration and interaction in MDRE and establishes
personalized requirements reuse in MDRE, consequently offers better
participation experiences for users.
1 Introduction
In many surveys conducted so far such as [STANDISH 95, 99], lack of user input
took the most responsibilities for software project failure. Nowadays, software
systems, instead of being attachments of hardware systems, are becoming more and
more interweaved with people, organizations, and social systems. Consequently, the
users we face are becoming more and more:
• complex in organizational structure, workflow relationships, and dynamic
interactions
• hierarchical in organizational roles
• specialized in knowledge body
• fuzzy-headed in what the software system they need will look like
All these bring new challenges in how to elicit user input correctly and completely.
We argue that attention should be paid to consider how to carry out effective
collaborations and interactions with users from the very beginning of the software life
cycle, that is, the requirements elicitation (RE) phase [Li 00].
In the RE state of art, the analysts typically drive RE process; users are just
passively involved in. This may partly due to the neglect of user participation in
traditional RE approaches. Additionally, the requirements reuse approaches appeared
in literature, such as the operational approach [Darimont 97] and the analogical
Liu H., Li C., Wang J., Wang Q. and Li M. (2004).
A User-Oriented Model-Driven Requirements Elicitation Process based on User Modeling.
In Proceedings of the 1st International Workshop on Computer Supported Activity Coordination, pages 174-184
DOI: 10.5220/0002647301740184
Copyright
c
SciTePress
approach [Massonet 97], did not provide user-oriented practice guide for dealing
interactions with users.
To cooperate with users with the characteristics mentioned above, we identified
two possible relevant vacancies in RE arena due to the methodological overlook of
user participation:
1. Absence of user-oriented RE process: most existed RE approaches do without
the recognition of internal structures of users, which partly results in ad hoc user
participation.
2. Absence of adaptive/personalized requirements reuse: in complex social systems,
users in different organizational positions with different backgrounds possess
different knowledge body and interests. On the other hand, today’s overload of
information often makes information systems ineffective. What of importance is
to deliver ‘right knowledge’ to ‘right person’. In RE process, requirements reuse
promises many benefits. However, we should not promise these benefits, in turn,
to our users while only relying on the experiences of analysts to perform such
personalization.
In this paper, we adopt user modeling techniques into RE, specifically
Model-Driven Requirements Elicitation method (MDRE), enhancing MDRE process
into a user-oriented one, and at the same time personalizing the requirements reuse
pattern of MDRE. We utilize stereotyped user modeling [Rich 89] and user-relation
modeling to provide workflow management of user RE process, and employ user
preference modeling to support personalized requirements reuse.
The paper is organized as follow. In Section 2 and 3, MDRE and user modeling
techniques are briefly introduced and summarized, respectively. In Section 4, our
approach combining these two techniques is elaborated in detail with three subsection,
namely 4.1 overall user-oriented process model, 4.2 MDRE workflow definition
language and 4.3 implementing techniques for personalized requirements reuse. The
first subsection 4.1 gives an overview of our approach and the corresponding process.
The next two subsections 4.2 and 4.3 present the technical details and the choices we
made in designing and implementing MDRE workflow management and personalized
requirements reuse. In Section 5, conclusions are made and future work of our
research is introduced.
2 Model-Driven Requirements Elicitation (MDRE)
MDRE originates from the ideas of knowledge representation, that from the cognitive
perspective, the world is considered as instances of some abstract concepts. Examples
of such concepts include entity, action, condition, event and so on. In 1986, this
concept-based idea was introduced into requirements elicitation and modeling with
the pioneer work of S. Greenspan [Greenspan 86] in RML (Requirements Modeling
Language). Up-to-date, several important MDRE methods have been proposed in the
literature, such as goal-directed requirements elicitation methods: KAOS [Dardenne
93], I* [Chung 00] and Scenario-based method: CREWS [Maiden 98].
MDRE method is based on a three-layer model architecture. The three models are
175
meta model, domain model and instance model respectively. Meta model, which is
composed of abstract concepts and their relations, is domain independent, and can be
regarded as the oracle of MDRE method, which conceptually drives the MDRE
process. Domain model, an instance of meta model in certain domain, captures
common characteristics of entities and relations in the domain of interest. Instance
model, in turn an instance of domain model, is a model of entities and relations for a
specific software system and its environment. The abstract level decreases from meta
model to instance model. Fig. 1 illustrates the three models with a purchase operation
in instance level.
Agent
Check-out
Customer
Action
Object
Product
ID
Product Copy
Perform
Input
relationship
P
e
r
f
o
r
m
I
n
p
u
t
stock
Lily,
platinum
Customer
Check-
out:time
Book:
TP31
TP31 No.110
stock
P
e
r
f
o
r
m
I
n
p
u
t
Instantiate
Instance
model
Domain
model
Meta model
Fig. 1 three-layer architecture of MDRE
We can see that certain MDRE method distinguishes itself by the constituents of its
meta model, which determines the way of thinking of analysts who perform RE
activities. We can say, most RE methods contain a meta model, whether explicitly or
implicitly. For example, in structured analysis, meta model includes data and process
as concepts; while in object-oriented paradigm, the concepts in its meta model include
object, message and so on. A MDRE method, besides a meta model which dictates
what to elicit, contains an elicitation strategy as another important component which
defines how to elicit. The strategy describes specific steps on how to find instances of
concepts defined in meta-model in problem domain. In goal-directed method,
elicitation strategy kicks off on finding the instances of the concept ‘goal’, or say goal
refinement. In scenario-based method, elicitation strategy advises recognizing
scenarios first, which in fact belong to the instance model, and then acquire instances
in domain-model through abstraction from scenarios.
3 User Modeling Techniques
User modeling is usually tracked back to the end of 70's last century [Perrault 78].
After decades, especially in recent years when the importance of user adaptive
systems is highly recognized, numerous application systems are developed based on
user modeling techniques.
User Modeling techniques concern mainly on modeling of user's category, property,
176
plan and preference in order that software systems could adaptively fit the needs of
different users. Traditional modeling techniques can be used in modeling user
category and property. It's more difficult to model user's plan because of the
combinatorial explosion to determine user’s goal from casual user action. In the
modeling of user preference, users' behavior (interaction with software systems) is the
main source to infer the interests of users. At first, natural language processing is the
most frequent used technique in collecting user information. Now many alternative
information sources are identified and are more effective than natural language
processing, e.g., user's interactions with GUI, hit sequence of hypertext links and/or
the user’s queries with databases.
User modeling has been successfully applied in many application areas, including
library reservation systems, user context-sensitive help systems, user-sensitive
navigation systems, adaptive websites and user sensitive filters.
4 Incorporating User Modeling Techniques into MDRE
Our approach offers two improvements to MDRE process by incorporating user
modeling techniques: 1) setup workflow management to facilitate user collaboration
and interaction in MDRE; 2) establish personalized requirements reuse in MDRE.
In complex user environment, static user relations have strong effect on the RE
workflow between users. So recognize user models containing user relations before
enacting RE activities can facilitate both multi-users RE workflow management and
the integration of the elicitation strategy of MDRE method into multi-user
environment. In our approach, we use stereotyped user modeling and user-relation
modeling to capture the underlying user models in multi-user environment. These user
models, combined with the elicitation strategy of MDRE method, are used to help
define MDRE workflow before the enactment of RE activities. Finally, a workflow
engine, dispatching and maintaining tasks among multi-users, supports the enactment
of predefined MDRE workflow.
As mentioned above, providing adaptive/personalized services to users is important
in reusing domain knowledge in complex user environment. In our approach, we
provide a context-based mechanism for implementing personalized requirements
reuse because we believe the exact knowledge a user needed is determined by some
contextual factors. We use three contextual factors among others for deciding what
information is more relevant to users in context. The three contextual factors are 1)
user-specific behaviors, 2) user stereotype, and 3) user’s task at hand.
4.1 Overall User-Oriented Process Model
Fig. 2 illustrated the overall process model of our user-oriented approach of
integrating user modeling techniques and MDRE. The MDRE process consists of four
steps and is accompanied by a domain knowledge base. We can see in Fig. 2 that the
MDRE method is a plug-in component, thus the architecture is flexible enough for
177
adopting new MDRE methods. Before we go to details of the four steps, we briefly
introduce the components of the domain knowledge base of their contents and usages.
User Preference Base
User
1
User
2
User
3
User
4
User Models
MDRE
Work-
flow
Defini-
tion
Domain Model
Personalization Component
Meta Model
Acquisi-
tion
Strategy
Domain Ontology
Instance Model
MDRE Method
Domain User Base
User Behavior
Domain Knowledge Base
MDRE Process
1.User Modeling
2.MDRE Workflow Definition
4.User Behavior Feedback
3.Enactment of MDRE
Workfolw
(With Personalized
Requirements Reuse Support)
MDRE Workflow
...
...
...
...
...
...
...
User-
Relation
Stereotype
Stereotype
Stereotype
...
...
...
User-
Relation
Instantiate
Data Flow
(1)
(7)
(8)
(3)
(2)
(9)
(4)
(5)
(6)
(10)
Fig. 2 Overall User-Oriented Process Model
Domain User Base: Domain User Base ((1) in Fig. 2) contains user stereotypes and
possible user-relations in domain of interest.
User Preference Base: User Preference Base ((2) in Fig. 2) contains user preferences
data of all stereotyped and non-stereotyped users.
Domain Model: Domain model ((4) in Fig. 2) is the second level model of the
MDRE three-layer architecture.
Instance Model: Instance model ((5) in Fig. 2) is the third level of the MDRE
three-layered architecture.
Domain Ontology: Domain ontology ((6) in Fig. 2) contains the factual ontology in
domain of interest, namely the concepts and their semantic relationships.
Now is the illustration about how the process works:
1. User Modeling: Define User Models by instantiating and tailoring the domain
user base ((7) in Fig. 2)
2. MDRE workflow definition: define MDRE workflow in comply with
user-relations in user models and elicitation strategy of MDRE method ((8) in
Fig. 2)
3. Enactment of MDRE Workflow (with Personalized Requirements Reuse Support):
the actual RE activities with the support of workflow engine and domain
knowledge base
4. User Behavior Feedback: record and analyze user behavior in RE activities to
accomplish evolution process of domain knowledge base
178
4.2 MDRE Workflow Definition Language
The workflow definition language we used contains only a small subset of modeling
elements of traditional process modeling languages (such as SLANG, SPADE in
[Armenise 93]). In this small language, process, task, role are three basic modeling
elements:
Role: an abstract user assigned with some tasks.
Task: the atomic unit of the process. Task must be associated with some role(s). To
indicate the status of the task, it can carry a return value of Boolean or Integer type.
We define 4 temporal relations between tasks: Begin-Begin (BB), Begin-End (BE),
End-Begin (EB), and End-End (EE). For example, if Task
1
and Task
2
have BB
relation, then the start point of task
2
must be later than the start point of task
1
.
Process: the network of tasks and their relations.
The language ignores the input/output of both tasks and processes in order to ease
the access of documents and work products among users. A potential shortcoming of
this choice is users have to take the responsibilities of maintaining the consistency
between documents and work products. Luckily, it won’t be a tough problem if using
some configuration tools. In the workflow definition language, role is abstract user.
Specific user must be filled in during instantiation. For example in a subordinate
relation, there are only two roles: superior and junior. In workflow enactment, these
abstract roles must be binding to some concrete users.
4.3 Implementation Techniques for Personalized Requirements Reuse
The personalized requirements reuse support is based on three contextual factors: 1)
user-specific behaviors, 2) user stereotype, and 3) user’s task at hand. The techniques
engaged in implementing context-based personalization are: stereotype-based
collaborative filtering, ontology-based semantic search, rule-based user preference
revision. The implementation framework using this technique is illustrated in Fig. 5.
Context is in the left box, containing user behaviors, task description stereotype and
corresponding user preference. As we can see in Fig. 5, user can get two kinds of
knowledge support, task-specific knowledge and preference knowledge. Task-specific
knowledge is derived from task description, while preference knowledge comes from
user stereotype and user behavior.
The process of generating preference knowledge:
1． Retrieve all preference records of past users with the same stereotype;
perform collaborative filtering [herlocker 99] to predict the user’s domain
preference based on those history records and the user’s initial profile.
2． With the user preference, perform ontology-based semantic search on
domain model to retrieve most relevant items.
3． In the RE activities, user behaviors are recorded, with which we can use
rule-based revision to dynamically adjust the user’s preference to count in
user-specific behavior contextual factor.
179
The process of generating task-specific knowledge:
1． Acquire task property vector by performing ontology-based semantic search
on task description
2． With the task property vector, perform ontology-based semantic search on
domain model to retrieve most task-relevant items.
User
Preference
Task
Property
Semantic
Search
CF
Domain
Ontology
Domain Model
User Preference Base
User
Preference
Semantic
Search
User
Stereotype
Task-Specific
Knowledge
Preference
Knowledge
Semantic
Search
Task
Description
User Behaviors
Context
Rule-
Based
Revi-
sion
Fig. 5 the Implementation Framework of Personalized Requirements Reuse
Before we introduce the techniques in detail, some structures are first introduced as
follow:
User preference vector: the user preference vector keeps the mapping from a user (u
i
)
to some concepts in domain ontology, which measures the users interests of those
concepts. The first row in Table 1 is the concepts c
i
, the second row is the relative
preference score s
r
(c
i
) of u
i
to each concept. The range is from 0 to 100.
Table 1 User Preference Vector
C
1
c
2
c
3
· ·
c
n
S
r
(c
1
) S
r
(c
2
) S
r
(c
3
)
· ·
S
r
(c
n
)
Task property vector: Task property vector shows whether a concept is relevant to
current task. If so, the score of the concept equals to 100, otherwise the score is 0.
Similar to the user preference vector, the first row in Table 2 is the concepts c
i
, the
second row is the relative preference score s
t
(c
i
) of current task to each concept.
Table 2 Table of task property
c
1
c
2
c
3
· ·
c
n
S
t
(c
1
) S
t
(c
2
) S
t
(c
3
)
· ·
S
t
(c
n
)
Domain ontology: domain ontology contains all the factual ontology in the domain of
interest, namely the concepts and the their relations in domain of interest. Three
semantic relationships are selected out: synonymy, generic, and specific semantic
relation.
180
1. Predict user preference with collaborative filtering
If a user u
a
‘s preference p
a,j
to a concept c
j
is not available in the initial user profile,
we can predict it with the following formula:
∑
=
−+=
n
i
i
ji
a
a,j
vvjawvp
1
_
,
_
))(,(
κ
①
In formula ①, all the user preference records of the same stereotype in the user
preference base are collaboratively considered to predict u
a
‘s preference. v
i,j
represents u
i
’s preference to a domain concept c
j
.
κ
is a normalization factor.
i
v
_
is
the average value user u
i
to all the domain concepts, it can be computed with the
following formula:
∑
∈
=
i
Ij
ji
i
i
v
I
v
,
_
||
1
②
In ②, I is the set composed of all the domain concepts to which u
a
’s preference is
not Ф.In ①, w(a,i) is the similarity degree between user u
a
and u
i
. We computes this
similarity with Pearson coefficient [Resnick 94], the formula is:
∑∑
∑
−−
−−
=
jj
i
ji
a
ja
j
i
ji
a
ja
vvvv
vvvv
iaw
2
_
,
2
_
,
_
,
_
,
)()(
))((
),(
③
2. Ontology-based Semantic search
Ontology-based semantic search computes the correlative degree between each
item in domain model and domain concepts in domain ontology, then assigns a score
to each item based on user preference vector. The score indicates a user’s possible
interests concerning a particular item.
Most domain concepts are not isolated. each has some semantic relations with
others (In domain ontology, such relations include synonymy, generic, and specific
semantic relation. For each concept c
i
, so called “semantic family” is composed of all
concepts which have either relations with it). We believe when considering the
correlation between an item in domain model and a particular concept in domain
ontology, it’s better and more natural to count in not only the concept ontology itself
but also its semantic family. Table 3 is an example of a concept c
i
’s semantic family.
Table 3 concept c
i
’s semantic family.
c
i1
c
i2
c
i3
· ·
c
ik
h(c
i1
) h(c
i2
) h(c
i3
)
· ·
h(c
ik
)
1
1
cc
w
21
cc
w
31
cc
w
· ·
k
cc
w
1
In table 3, the first row is the concepts in the semantic family of concept c
i
. The
second row denotes the scores of every correlative type, namely synonymy, generic
181
and specific. The third row is the weights of correlation between concept c
ij
and c
i
. All
these values are stored in domain ontology.
Before the algorithm, we first introduce some definitions:
G
0
= {c
i
| 1≤i≤n
c
, (n
c
is the number of domain concepts in user preference vector)
G
c1
= {b | b is the domain concept which has synonymy relation with concept c}
G
c2
= {b | b is the domain concept which has generic relation with concept c }
G
c3
= {b | b is the domain concept which has specific relation with concept c }
I = {c | c is relevant with item i}
k
c,j
is the number of keywords in concept c which are matched in item
i
. For
example, if key(c) is the set of keywords in concept c and key(item
i
) is the set of
keywords in item
i
, then k
c,i
= |key(c)∩key(item
i
)|.
For item
i
, we compute its score when regarded as preference knowledge and
task-specific knowledge (denoted as h
r
(item
i
) and h
t
(item
i
)) with the following two
formulas respectively:
() () ()
}{)(
0
3
1
∑∑∑
∩∈=∩∈
′
′
⎥
⎦
⎤
⎢
⎣
⎡
⋅
′
⋅
′
+⋅=
GIclGIc
iciicirir
cl
kcwcskcsitemh
κ
④
() ( ) ( )
}{)(
0
3
1
∑∑∑
∩∈=∩∈
′
′
⎥
⎦
⎤
⎢
⎣
⎡
⋅
′
⋅
′
+⋅=
GIclGIc
iciicitit
cl
kcwcskcsitemh
κ
⑤
In ④ and ⑤, the first part of the equation computes the relevant scores of item
i
to
concept c, the second part computes the relevant scores of item
i
to the semantic family
of concept c. k is a normalization factor.
3. Rule-based user preference revision
When dynamically adjusting user preference, we need to compute two ratios for a
particular domain concept c
i
. The first one is the percentage the score of c
i
to the sum
of all domain concepts’ preference scores:
∑
=
=
c
n
j
jrir
cscsT
1
1
)()(
(n
c
is the
number of domain concepts in user preference vector). The second one is the
percentage of actual accessing times of each domain concept to the sum of the times
all the concepts are actually accessed within a period of user RE activities (multiple
domain concepts might be involved in one access of an item):
∑∑∑
===
=
cii
n
i
n
j
ici
n
j
ici
itemsitemsT
111
2
)()(
（n
i
is the total number of the domain
concepts’ actual accessed times.）. The function s
ci
(item
i
) is defined as follow:
if (key(ci)∩key(itemi)≠Ф) s
ci
(item
i
) = 1 else s
ci
(item
i
) = 0;
182
Define ∆T=T
2
– T
1
. User preference revision rules are defined as follow:
Rule1. |∆T|≤0.1, the predictive result is proper and we need not adjust it this time.
Rule2. |∆T|>0.1, c
i
should be adjusted. The revision formula is
)()1()(
irir
csTcs ƥ+=
′
λ
, in which λ is the domino effect zooming factor and
could be adjusted based on practical experience.
5 Conclusions and Future work
In this paper, we introduced a novel RE approach, which, by incorporating user
modeling techniques, generates better user participation experiences. To be more
specific, the MDRE workflow management based on user models automates and
facilitates MDRE activities in multi-user environment; the personalized requirements
reuse based on context promotes the effectiveness and the efficiency of domain
knowledge reuse by providing users appropriate knowledge in appropriate occasion.
Finally, we list out some future work of this research: refine the prototype CASE
tools we developed so far to further demonstrate its use. Integrate existed
requirements engineering tools or languages such as UML. Build the structure of
domain ontology into domain model to support user-friendly query and provide
stronger reasoning capability of the domain knowledge base.
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