An Experimental Comparison of ER and UML Class Diagrams for Data Modelling - Experimental Material -

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1 An Experimental Comparison of ER and UML Class Diagrams for Data Modelling - Experimental Material - January 14, 2009 Abstract This report describes the experimental material used in three sets of controlled experiments carried out to compare ER and UML class diagrams for data modelling. In particular, the experimentation aimed at comparing the support given by ER and UML class diagrams in comprehension, maintenance, and verification of data models. The experiments involved university students with different levels of ability and experience. The comparison provides qualitative and quantitative results that can be used by project managers to evaluate the possibility of adopting a design method within their own organisation, depending on the skills of the involved human resources.

2 1 Comprehension Tasks: questionnaire and artefacts This section describes the two tasks used to analyse the comprehensibility of ER and UML class diagrams. To evaluate it, we asked the subjects to answer a questionnaire consisting of 5 multiple choice questions where each question can have one or more correct answers. It is important to note that the number of answers was the same for each question (i.e., three answers), while the number of correct answers was different. The questions cover all the entities and the relationships of the data model presented to the subjects. Next section shows the questionnaire and the ER and UML class diagrams (see Figure 1) for the task T1 c on the data model ADAMS-TeamManagement. Moreover, Section 1.2 shows the ER and the UML class diagrams (see Figure 2), as well as the questionnaire, for the task T2 c on the data model EasyClinic-BookingManagement. 1.1 Task T1 c The questionnaire used for the ADAMS-TeamManagement system is: Q1 Consider the relationship between Artefact and Version and select the correct statements: An artefact can have more versions An artefact can have at most one version An artefact could have no versions Q2 Consider the relationship between Artefact and Resource and select the correct statements: On an artefact can be allocated one resource On an artefact can be allocated at least one resource On an artefact could be no resources allocated Q3 Consider the relationship between Version and File and select the correct statements: A version can have more associated files A version could be no associated files A version can have at most one associated file Q4 Consider the class Resource and its relationships. Which are the correct statements: Skills of a resource can be identified It is possible to verify if a resource is allocated on an artefact It is possible to identify the telephone number of a resource

3 Figure 1: Data model of ADAMS-TeamManagement represented by an ER diagram and an UML class diagram Q5 Consider the class Artefact and its relationships. Which are the correct statements: An artefact can be associated to only one project

4 Figure 2: EasyClinic data model represented by ER diagram and UML class diagram It is possible to identify the artefact manager It is possible to identify the date of an artefact version 1.2 Task T2 c The questionnaire used for the EasyClinic-BookingManagement system is: Q1 Consider the relationship between Patient and Booking and select the correct

5 statements: A patient can make only one reservation A patient has to make at least one reservation A patient could not make a reservation Q2 Consider the relationship between Patient and Visit and select the correct statements: A patient can make only one visit A patient has to make at least one visit A patient can make more than one visit Q3 Consider the relationship between Booking and VisitType and select the correct statements: A reservation has to refer to only one type of visit A reservation could not refer to any type of visit A reservation is referred to at least one type of visit Q4 Consider the class Patient and its relationships. Which are the correct statements: It is possible to establish the reservations of a patient It is possible to establish when a patient has been registered It is possible to establish the reservation cancelled by a patient Q5 Consider the class Booking and its relationships. Which are the correct statements: A reservation can be made by more than one patient Given a reservation, it is possible to establish the of the booked visit Given a reservation, it is possible to establish the date of the visit

6 2 Maintenance Tasks: questionnaire and artefacts This section describes the two tasks used to analyse the maintainability of ER and UML class diagrams. In order to evaluate it we adopted a similar approach as the assessment of the comprehension level. In particular, we asked the subjects to answer a questionnaire consisting of 5 multiple choice questions, but in this case each question has only one correct answers. It is important to note that the number of answers was the same for each question (i.e., three answers). In each question we present a change request and ask to the subjects to select which are the correct changes to perform on the data model to satisfy the request. Next section shows the questionnaire and the UML class diagram (see Figure 3) for the task T1 m on the data model Company. Moreover, Section 2.2 shows the ER diagram (see Figure 10), as well as the questionnaire, for the task T2 m on the data model University. Figure 3: Company data model represented by UML class diagram 2.1 Task T1 m The questionnaire used for the Company system is: Q1 We want to keep track of the projects completed by each unit (by storing start and end date of the project). What are the modifications to be accomplished in order to carry out this request? Select the correct UML class diagram in Figure 2.1:

7 WorksOn hour Projects location controls works_on Startdate chairs +supervised supervises Projects location controls CompleteProjects works_for Manager companyphone companycar projectbenefit +supervisor Developer nolanguages completeprojects Question Q1 Projects location CompleteProjects Projects location CompleteProjects Projects location controls controls controls 1 completeprojects 1 completeprojects Question Q2 Projects location Figure 4: Question Q1 - Select the correct UML class diagram 1 1 controls depend 1 Q2 We want to keep track of the dependent people for each employee, by storing DependentOf Social Security Number (SSN), first, last, birth of date. What are the modifications to be accomplished in order to carry out this request? Select the correct UML class diagram in Figure 2.1: Question Q2 1 1 depend DependentOf depend DependentOf 1 1 depend DependentOf depend Question Q3 Figure 5: Question Q2 - Select the correct UML class diagram DependentOf worked Worked

8 1 1 depend DependentOf Q3 We want to keep track of all unit for which an employee worked, worked by storing the start date and the end date (note that that an employee can work for a department at most once and an employee works for one and only department at a given date). What are the modifications to be accomplished in order to carry out this request? Select the correct UML class diagram in Figure 2.1: Question Q3 1 1 Worked worked Worked 1 1 worked Worked worked Worked Question Q4 Figure 6: Question Q3 - Select the correct UML class diagram Worked Q4 We want to keep track of the seniority years of the manger and developers. What worked are the modifications to be accomplished in order to carry out this request? SSe- Manager Developer companyphone nolanguages lect the correct UML class diagram companycar inseniority Figure 2.1: projectbenefit seniority Question Q4 seniority seniority Manager Developer Manager Developer Manager Developer companyphone companycar projectbenefit seniority nolanguages seniority companyphone companycar projectbenefit nolanguages companyphone companycar projectbenefit seniority nolanguages seniority seniority Figure 7: Question Q4 - Select the correct UML class diagram Manager companyphone companycar projectbenefit Developer nolanguages Q5 Consider the database schemas before and after a maintenance activity on the relational schemas PROJECTS e UNIT (see Figure 8). Note that the attributes with a line are the primary keys while the starred attributes are reference keys. Select the correct UML class diagram (regarding PROJECTS e UNIT classes) from Figure 2.1 for the relational schema after the maintenance activity.

9 Figure 8: Company Schema before the maintenance activity and after the maintenance activity Figure 9: Question Q5 - Select the correct UML class diagram

10 Vote Registration STUDENT Date Presence ATTENDS Figure 10: University data model represented by ER diagram 2.2 Task T2 m Registration Question Q2 Presence The questionnaire STUDENT used ATTENDS for the University system is: Vote Date Q1 We want to keep track of the module completed by each student, storing the vote and the date. What are the modifications to be accomplished in order to carry out this request? Select the correct ER diagram in Figure 2.2: Question Q2 (0,1) Question Q3 Figure 11: Question Q1 - Select the correct ER diagram TEACHES TEACHES TEACHES

11 Vote Registration STUDENT Date ATTENDS Question Q2 Presence Registration STUDENT ATTENDS Vote Date Q2 We want to keep track of the information on the lessons for each module by storing room, floor, and hour. What are the modifications to be accomplished in order to carry out this request? Select the correct ER diagram in Figure 2.2: Question Q2 (0,1) (0,1) Question Q3 (0,1) Figure 12: Question Q2 - Select the correct ER diagram Question Q3 TEACHES Q3 We want to keep track of all teacher that teach a Module, by storing their responsability (0,1) and the number Question ofq3 hour (taking into account that a module can be held by more than one teacher). What are the modifications to be accomplished in TEACHES order to carry out this request? Select the correct ER diagram in Figure??: TEACHES Question Q3 TEACHES TEACHES TEACHES TEACHES TEACHES TEACHES TEACHES TEACHES TEACHES Figure 13: Question Q3 - Select the correct ER diagram Q4 We want to keep track of the telephone number of teachers and students. What are the modifications to be accomplished in order to carry out this request? Select the correct ER diagram in Figure 2.2:

12 Question Q4 Registration STUDENT SSN Last Address SSN First Last Address First Registration Registration STUDENT STUDENT SSN Registration SSN Last STUDENT Last Address SSN Address First First Address Last First Question Q4 SSN Last Address First Registration STUDENT SSN Last Address First Registration SSN STUDENT Last Address First Registration SSN STUDENT Last Address First STUDENT relational schemas Faculty and Department in Figure 15. Note that the attributes Figure 14: Question Q4 - Select the correct ER diagram Registration STUDENT Registration Q5 Consider the database schemas before and after a maintenance activity on the with a line are the primary keys while the starred attributes are reference keys. Select the correct ER diagram (regarding Faculty and Department entities) from Figure 2.2 for the relational schema after the maintenance activity

13 Figure 15: Company Schema before the maintenance activity and after the maintenance activity Figure 16: Question Q5 - Select the correct ER diagram

14 3 Verification Tasks: questionnaire and artefacts This section describes the two tasks used to analyse the support give by ER and UML class diagrams during verification activities. In order to evaluate it we presented to the subjects a list of requirements and asking them to highlight in the data models the points that did not satisfy the requirements. Next section shows the requirements and both the ER and UML class diagram (see Figures 3.1 and 3.1) for the task T1 v on the data model ADAMS-EventManagement. Moreover, Section 3.2 shows both the ER and UML class diagrams (see Figures 3.1 and 3.1), as well as the requirements, for the task T2 v on the data model EasyClinic- VisitManagement. 3.1 Task T1 v The following diagram represents the data model of an artefact management system, called ADAMS.In particular, the diagram describes the management of the files associated to an artefact and the event subscriptions mechanism of ADAMS. The diagram contains some defects, e.g., missing attributes or relationships, wrong cardinality. Analyse the requirements of the system and highlight in the data models the points that do not satisfy the requirements Figure 17: UML class diagram of ADAMS-EventManagement An artefact...

15 Figure 18: ER diagram of ADAMS-EventManagement is characterised by a, a description, a status, a creation data, a starting and ending date; has a type. The artefact type is characterised by a, a description, an icon, and an identifier. Moreover, almost a file type has to be specified for each artefact type. Clearly, the same file type (characterised by a, a description and an extension) can be associated to one or more artefact types; should depend by other artefacts (target). In this case, it is necessary to specify the direction as well as the stereotype of the dependence; should be composed of one or more artefacts. In this case, for each component artefacts (child) it is necessary to specify its position in the hierarchy; has at least one resource allocated on it. Each resource allocated on an artefacts has the possibility to subscribe an event on it specifying the subscription level (eventlevel). 3.2 Task T2 v The following diagram represents the data model of a software system implementing all the operations required to manage a doctor s office, called EasyClinic.In particular, the diagram describes the management of the patients visits and bookings. The diagram contains some defects, e.g., missing attributes or relationships, wrong cardinality.

16 Figure 19: UML class diagram of EasyClinic-VisitManagement Figure 20: ER diagram of EasyClinic-VisitManagement Analyse the requirements of the system and highlight in the data models the points that do not satisfy the requirements.

17 A visit... is characterised by a date, a code, an anamnesis, and a therapy; should require some laboratory exams. In this case is specified when the exam is performed (i.e., date) and the results of the exam. Clearly, the same exam should be required in one or more visit. Each exam is characterised by a and a description, and it is performed in a laboratory. Each laboratory is characterised by a and an. Moreover, each laboratory is specialised in several exams and only one laboratory is able to perform a particular exam; is performed by at least one doctor. In this case is specified the role of the doctor; requires a booking. Clearly, a booking should exist without a visit (it is not performed yet).