9.6 Developing an OO Database Application

The process of creating an OO database application using an OODBMS is meant to be a natural extension of application development in an OO programming environment. As discussed previously, there are language bindings specified in the ODMG standard for C++, Java, and Smalltalk, as well as other language bindings. The difference between using objects in programs written in these languages and database objects is the persistence of the database objects. Vendors that support the ODMG standard provide facilities to make program objects persist and to provide access to database objects for manipulation within programs.

Current OODBMS products include systems such as InterSystems Iris, Objectivity/DB, Matisse, GemStone/S, ObjectStore, Actian NoSQL, Perst, ZODB, ObjectDB, and ObjectDatabase++. The specific characteristics and functionality of each system vary, but these systems generally support the object data model together with access from a multitude of programming languages, such as C++, C#, Java, Smalltalk, and Python. Application development is typically supported from various integrated data environments with capabilities for querying data through an OQL-like or SQL-like query language. In this section, we highlight the application development capabilities of InterSystems Iris as an example of an OODBMS and also revisit the University schema within the Iris object data model.

9.6.1 Overview of InterSystems Iris

FIGURE 9.7 provides a high-level overview of the InterSystems Iris Data Platform. Iris is a multimodel system, supporting the ODMG object model as well as relational tables, document data, and key-value pair data. Iris has been designed to support interoperability among these different data representations in addition to support for the object data model. Our focus is on Iris support for objects.

The Inter Systems Iris Data Platform consists of Cube, Tables, Documents, and Key value. The 4 blocks connected to the Inter Systems Iris Data Platform are Application Development, Terminal, Management Portal, and Application Code. Application Development block consists of Visual Studio Code, Docker, Iris Studio, and Open Exchange. Terminal consists of Object script Command Line plus S Q L access. Management Portal consists of Systems Administration plus S Q L access. Application code consist of Application Programming Interfaces A P I s and O D B C slash J D B C drivers.

FIGURE 9.7 The InterSystems Iris Data Platform

As shown in Figure 9.7, application development with Iris can be performed with tools such as Visual Studio Code and Docker. These tools provide environments for creating object schemas and developing software applications that access Iris OO data with extensions that support ObjectScript, an embedded programming language for objects developed by InterSystems. Iris Studio provides wizards for assistance in creating ODL class declarations that include inheritance specifications together with attribute, relationship, and method definitions. InterSystems also provides an Open Exchange repository for developers, where developers can share tools for working with Iris data. One such tool is RAD (Rapid Application Development) Studio, providing a way to quickly create forms for inserting and manipulating Iris objects. Other notable tools in the Open Exchange are Class Explorer, providing a UML-like view of Iris class definitions, and Web Terminal, providing a web-based terminal for access to Iris data. The Iris Terminal is a command-line interface that can be operated in two different modes. In its basic mode, objects can be created, stored, and retrieved using ObjectScript. The Iris Terminal can also be operated in the SQL Query Shell mode, where SQL can be used to query object classes viewed as relational tables. As in OQL, SQL within InterSystems Iris supports an implicit join feature for traversing object relationships. The Iris Management Portal also supports an SQL query capability in addition to general systems administration capabilities for managing user access to the data platform. The query capabilities in the Iris Terminal and the Management Portal can be used for ad-hoc queries or to test query access for further use in application development.

Figure 9.7 also illustrates that InterSystems supports Application Programming Interfaces (APIs) that use ODBC and JDBC drivers. Languages supported include Java and Python, as well as development environments such as .NET and Node.js. The InterSystems APIs include a JDBC driver API for access to relational tables or to object classes when viewed as relational tables, the XEP (Express Event Persistence) API for inserting and accessing object data, and a Native API for direct access to data such as NoSQL key-value pair data (a data format described in Chapter 14), or data stored in XML or JSON format (data formats described in Chapter 13). There are many other features of the Iris Data Platform that are beyond the scope of this chapter. Readers are encouraged to explore the InterSystems website to learn more about Iris support for objects and interoperability with other data representations.

9.6.2 Schema Definition in Iris

FIGURE 9.8 shows the class definitions for the revised University schema that corresponds to the UML diagram in Figure 9.5, created using Iris Studio. The first class, Address, describes a serial object, which is an object that can be embedded in other classes. For example, Address is used as the type of the addr attribute in the Person class that follows. This is similar to the definition of Addr as Struct in the ODL definition of the University schema in Figure 9.6.

Line 1. Class University dot Address Extends open parentheses percentage Serial Object close parentheses open curly brace Line 2. Property Street As percentage String open parentheses MAX LEN equals 80 close parentheses semicolon Line 3. Property City As percentage String open parentheses MAX LEN equals 80 close parentheses semicolon Line 4. Property State As percentage String open parentheses MAX LEN equals 2 close parentheses semicolon Line 5. Property Zip As percentage String open parentheses MAX LEN equals 5 close parentheses semicolon Line 6. close curly brace Line 7. Class University dot Person Extends open parentheses percentage Persistent close parentheses open curly brace Line 8. Property p I d As percentage Integer open square bracket Required close square bracket semicolon Line 9. Index p I d Index On p I d open square bracket Unique close square bracket semicolon Line 10. Property l Name As percentage String open square bracket Required close square bracket semicolon Line 11. Property f Name As percentage String open square bracket Required close square bracket semicolon Line 12. Property a d d r As Address semicolon Line 13. Property phone As percentage String semicolon Line 14. Property birth Date As percentage Date semicolon Line 15. Method find Age open parentheses close parentheses As percentage Integer open curly brace close curly brace Line 16. close curly brace Line 17. Class University dot Faculty Extends Person open curly brace Line 18. Property rank As percentage String open parentheses VALUELIST equals double quotes Instructor comma Assistant comma Associate comma Professor double quotes close parentheses semicolon Line 19. Property salary As percentage Numeric semicolon Line 20. Relationship advises As University dot Student open square bracket Cardinality equals many comma Inverse equals has Advisor close square bracket semicolon Line 21. Relationship belongs To As University dot Department open square bracket Cardinality equals one comma Inverse equals has Faculty close square bracket semicolon Line 22. Relationship teaches As University dot Class Section open square bracket Cardinality equals many comma Inverse equals has Teacher close square bracket semicolon Line 23. Relationship has Evaluation As University dot Evaluation open square bracket Cardinality equals children comma Line 24. Inverse equals is Eval Of close square bracket semicolon Line 25. Method give Raise open parentheses close parentheses As percentage Numeric open curly brace close curly brace Line 26. close curly brace Line 27. Class University dot Student Extends University dot Person open curly brace Line 28. Property credits As percentage Small Int open square bracket Initial Expression equals 0 close square bracket semicolon Line 29. Property g p a As percentage Numeric open parentheses MAX VAL equals 4.0 comma MINVAL equals 0.0 close parentheses semicolon Line 30. Relationship has Advisor As University dot Faculty open square bracket Cardinality equals one comma Inverse equals advises close square bracket semicolon Line 31. Relationship takes Class As University dot Enrollment open square bracket Cardinality equals many comma Inverse equals student Line 32. Enrolled close square bracket semicolon Line 33. Relationship earned Grade As University dot Mark open square bracket Cardinality equals many comma Inverse equals given Student close square bracket semicolon Line 34. Method add Credits open parentheses num Credits As percentage Small Int close parentheses open curly brace close curly brace Line 35. Method get Status open parentheses close parentheses As percentage String open curly brace close curly brace Line 36. close curly brace Line 37. Class University dot Undergraduate Extends University dot Student open curly brace Line 38. Property major As percentage String semicolon Line 39. Method change Major open parentheses new Major As percentage String close parentheses open curly brace close curly brace Line 40. close curly brace Line 41. Class University dot Graduate Extends University dot Student open curly brace Line 42. Property program As percentage String semicolon Line 43. Method change Program open parentheses new Program As percentage String close parentheses open curly brace close curly brace Line 44. close curly brace Line 45. Class University dot Teaching Assistant Extends University dot Graduate open curly brace Line 46. Property funding Source As percentage String semicolon Line 47. Property tuition Remission As percentage Numeric semicolon Line 48. close curly brace Line 49. Class University dot Department Extends open parentheses percentage Persistent close parentheses open curly brace Line 50. Property dept Code As percentage String open square bracket Required close square bracket semicolon Line 51. Property dept Name As percentage String open square bracket Required close square bracket semicolon Line 52. Index dept Code Name Index On open parentheses dept Code comma dept Name close parentheses open square bracket Unique close square bracket semicolon Line 53. Property dept Office As percentage String semicolon Line 54. Property dept Phone As percentage String semicolon Line 55. Property has Chair As University dot Faculty semicolon Line 56. Index has Chair Index On has Chair open square bracket Unique close square bracket semicolon Line 57. Foreign Key has Chair F K open parentheses has Chair close parentheses References University dot Faculty open parentheses close parentheses semicolon Line 58. Relationship has Faculty As University dot Faculty open square bracket Cardinality equals many comma Inverse equals belongs To close square bracket semicolon Line 59. Relationship offers As University dot Course open square bracket Cardinality equals many comma Inverse equals is Offering close square bracket semicolon Line 60. close curly brace Line 61. Class University dot Course Extends open parentheses percentage Persistent close parentheses open curly brace Line 62. Property c No As percentage String open square bracket Required close square bracket semicolon Line 63. Index c No Index On c No open square bracket Unique close square bracket semicolon Line 64. Property c Title As percentage String open square bracket Required close square bracket semicolon Line 65. Property credits As percentage Small Int semicolon Line 66. Property description As percentage String semicolon Line 67. Relationship is Offering As University dot Department open square bracket Cardinality equals one comma Inverse equals offers close square bracket semicolon Line 68. Relationship has Section As University dot Class Section open square bracket Cardinality equals children comma Line 69. Inverse equals is Section Of close square bracket semicolon Line 70. Relationship has Pre Req As University dot Pre reqs open square bracket Cardinality equals many comma Inverse equals is Pre Req Of close square bracket semicolon Line 71. Relationship pre Req Of As University dot Pre reqs open square bracket Cardinality equals many comma Inverse equals is Pre Req close square bracket semicolon Line 72. close curly brace Line 73. Class University dot Pre reqs Extends open parentheses percentage Persistent close parentheses open curly brace Line 74. Relationship is Pre Req Of As University dot Course open square bracket Cardinality equals one comma Inverse equals has Pre Req comma Line 75. Required close square bracket semicolon Line 76. Relationship is Pre Req As University dot Course open square bracket Cardinality equals one comma Inverse equals pre Req Of comma Required close square bracket semicolon Line 77. Index pre reqs Index On open parentheses is Pre Req Of comma is Pre Req close parentheses open square bracket Unique close square bracket semicolon Line 78. close curly brace Line 79. Class University dot Class Section Extends open parentheses percentage Persistent close parentheses open curly brace Line 80. Property section Code As percentage String open square bracket Required close square bracket semicolon Line 81. Index section Code Index On section Code open square bracket Unique close square bracket semicolon Line 82. Property schedule As percentage String semicolon Line 83. Property room As percentage String semicolon Line 84. Property has T A As University dot Teaching Assistant semicolon Line 85. Index has T A Index On has T A open square bracket Unique close square bracket semicolon Line 86. Foreign Key has T A F K open parentheses has T A close parentheses References University dot Teaching Assistant open parentheses close parentheses semicolon Line 87. Relationship has Teacher As University dot Faculty open square bracket Cardinality equals one comma Inverse equals teaches comma Line 88. Required close square bracket semicolon Line 89. Relationship has Student As University dot Enrollment open square bracket Cardinality equals many comma Inverse equals class Taken close square bracket semicolon Line 90. Relationship is Section Of As University dot Course open square bracket Cardinality equals parent comma Inverse equals Line 91. Has Section comma Required close square bracket semicolon Line 92. Relationship given In As Universit dot Mark open square bracket Cardinality equals many comma Inverse equals given To close square bracket semicolon Line 93. close curly brace Line 94. Class University dot Enrollment Extends percentage Persistent open curly brace Line 95. Relationship student Enrolled As University dot Student open square bracket Cardinality equals one comma Inverse equals Line 96. Takes Class comma Required close square bracket semicolon Line 97. Relationship class Taken As University dot Class Section open square bracket Cardinality equals one comma Inverse equals Line 98. Has Student comma Required close square bracket semicolon Line 99. Index enrolment Index On open parentheses student Enrolled comma class Taken close parentheses open square bracket Unique close square bracket semicolon Line 100. close curly brace Line 101. Class University dot Evaluation Extends open parentheses percentage Persistent close parentheses open curly brace Line 102. Property eval Date As percentage Date open square bracket Required close square bracket semicolon Line 103. Property rater Name As percentage String open square bracket Required close square bracket semicolon Line 104. Property rating As percentage String open parentheses VALUELIST equals double quotes 1 comma 2 comma 3 comma 4 comma 5 double quotes close parentheses open square bracket Required close square bracket semicolon Line 105. Relationship is Eval Of As University dot Faculty open square bracket Cardinality equals parent comma Inverse equals has Evaluation close square bracket semicolon Line 106. Index eval Index On open parentheses eval Date comma is Eval Of close parentheses open square bracket Unique close square bracket semicolon Line 107. close curly brace Line 108. Class University dot Mark Extends open parentheses percentage Persistent close parentheses open curly brace Line 109. Property grade As percentage String open parentheses VALUE LIST equals double quotes A comma B comma C comma D comma F comma W comma I double quotes close parentheses semicolon Line 110. Relationship given Student As University dot Student open square bracket Cardinality equals one comma Inverse equals earned Grade comma Line 111. Required close square bracket semicolon Line 112. Relationship given To As University dot Class Section open square bracket Cardinality equals one comma Inverse equals given In comma Line 113. Required close square bracket semicolon Line 114. Index mark Index On open parentheses given Student comma given To close parentheses open square bracket Unique close square bracket semicolon Line 115. close curly brace

Line 1. Class University dot Address Extends open parentheses percentage Serial Object close parentheses open curly brace Line 2. Property Street As percentage String open parentheses MAX LEN equals 80 close parentheses semicolon Line 3. Property City As percentage String open parentheses MAX LEN equals 80 close parentheses semicolon Line 4. Property State As percentage String open parentheses MAX LEN equals 2 close parentheses semicolon Line 5. Property Zip As percentage String open parentheses MAX LEN equals 5 close parentheses semicolon Line 6. close curly brace Line 7. Class University dot Person Extends open parentheses percentage Persistent close parentheses open curly brace Line 8. Property p I d As percentage Integer open square bracket Required close square bracket semicolon Line 9. Index p I d Index On p I d open square bracket Unique close square bracket semicolon Line 10. Property l Name As percentage String open square bracket Required close square bracket semicolon Line 11. Property f Name As percentage String open square bracket Required close square bracket semicolon Line 12. Property a d d r As Address semicolon Line 13. Property phone As percentage String semicolon Line 14. Property birth Date As percentage Date semicolon Line 15. Method find Age open parentheses close parentheses As percentage Integer open curly brace close curly brace Line 16. close curly brace Line 17. Class University dot Faculty Extends Person open curly brace Line 18. Property rank As percentage String open parentheses VALUELIST equals double quotes Instructor comma Assistant comma Associate comma Professor double quotes close parentheses semicolon Line 19. Property salary As percentage Numeric semicolon Line 20. Relationship advises As University dot Student open square bracket Cardinality equals many comma Inverse equals has Advisor close square bracket semicolon Line 21. Relationship belongs To As University dot Department open square bracket Cardinality equals one comma Inverse equals has Faculty close square bracket semicolon Line 22. Relationship teaches As University dot Class Section open square bracket Cardinality equals many comma Inverse equals has Teacher close square bracket semicolon Line 23. Relationship has Evaluation As University dot Evaluation open square bracket Cardinality equals children comma Line 24. Inverse equals is Eval Of close square bracket semicolon Line 25. Method give Raise open parentheses close parentheses As percentage Numeric open curly brace close curly brace Line 26. close curly brace Line 27. Class University dot Student Extends University dot Person open curly brace Line 28. Property credits As percentage Small Int open square bracket Initial Expression equals 0 close square bracket semicolon Line 29. Property g p a As percentage Numeric open parentheses MAX VAL equals 4.0 comma MINVAL equals 0.0 close parentheses semicolon Line 30. Relationship has Advisor As University dot Faculty open square bracket Cardinality equals one comma Inverse equals advises close square bracket semicolon Line 31. Relationship takes Class As University dot Enrollment open square bracket Cardinality equals many comma Inverse equals student Line 32. Enrolled close square bracket semicolon Line 33. Relationship earned Grade As University dot Mark open square bracket Cardinality equals many comma Inverse equals given Student close square bracket semicolon Line 34. Method add Credits open parentheses num Credits As percentage Small Int close parentheses open curly brace close curly brace Line 35. Method get Status open parentheses close parentheses As percentage String open curly brace close curly brace Line 36. close curly brace Line 37. Class University dot Undergraduate Extends University dot Student open curly brace Line 38. Property major As percentage String semicolon Line 39. Method change Major open parentheses new Major As percentage String close parentheses open curly brace close curly brace Line 40. close curly brace Line 41. Class University dot Graduate Extends University dot Student open curly brace Line 42. Property program As percentage String semicolon Line 43. Method change Program open parentheses new Program As percentage String close parentheses open curly brace close curly brace Line 44. close curly brace Line 45. Class University dot Teaching Assistant Extends University dot Graduate open curly brace Line 46. Property funding Source As percentage String semicolon Line 47. Property tuition Remission As percentage Numeric semicolon Line 48. close curly brace Line 49. Class University dot Department Extends open parentheses percentage Persistent close parentheses open curly brace Line 50. Property dept Code As percentage String open square bracket Required close square bracket semicolon Line 51. Property dept Name As percentage String open square bracket Required close square bracket semicolon Line 52. Index dept Code Name Index On open parentheses dept Code comma dept Name close parentheses open square bracket Unique close square bracket semicolon Line 53. Property dept Office As percentage String semicolon Line 54. Property dept Phone As percentage String semicolon Line 55. Property has Chair As University dot Faculty semicolon Line 56. Index has Chair Index On has Chair open square bracket Unique close square bracket semicolon Line 57. Foreign Key has Chair F K open parentheses has Chair close parentheses References University dot Faculty open parentheses close parentheses semicolon Line 58. Relationship has Faculty As University dot Faculty open square bracket Cardinality equals many comma Inverse equals belongs To close square bracket semicolon Line 59. Relationship offers As University dot Course open square bracket Cardinality equals many comma Inverse equals is Offering close square bracket semicolon Line 60. close curly brace Line 61. Class University dot Course Extends open parentheses percentage Persistent close parentheses open curly brace Line 62. Property c No As percentage String open square bracket Required close square bracket semicolon Line 63. Index c No Index On c No open square bracket Unique close square bracket semicolon Line 64. Property c Title As percentage String open square bracket Required close square bracket semicolon Line 65. Property credits As percentage Small Int semicolon Line 66. Property description As percentage String semicolon Line 67. Relationship is Offering As University dot Department open square bracket Cardinality equals one comma Inverse equals offers close square bracket semicolon Line 68. Relationship has Section As University dot Class Section open square bracket Cardinality equals children comma Line 69. Inverse equals is Section Of close square bracket semicolon Line 70. Relationship has Pre Req As University dot Pre reqs open square bracket Cardinality equals many comma Inverse equals is Pre Req Of close square bracket semicolon Line 71. Relationship pre Req Of As University dot Pre reqs open square bracket Cardinality equals many comma Inverse equals is Pre Req close square bracket semicolon Line 72. close curly brace Line 73. Class University dot Pre reqs Extends open parentheses percentage Persistent close parentheses open curly brace Line 74. Relationship is Pre Req Of As University dot Course open square bracket Cardinality equals one comma Inverse equals has Pre Req comma Line 75. Required close square bracket semicolon Line 76. Relationship is Pre Req As University dot Course open square bracket Cardinality equals one comma Inverse equals pre Req Of comma Required close square bracket semicolon Line 77. Index pre reqs Index On open parentheses is Pre Req Of comma is Pre Req close parentheses open square bracket Unique close square bracket semicolon Line 78. close curly brace Line 79. Class University dot Class Section Extends open parentheses percentage Persistent close parentheses open curly brace Line 80. Property section Code As percentage String open square bracket Required close square bracket semicolon Line 81. Index section Code Index On section Code open square bracket Unique close square bracket semicolon Line 82. Property schedule As percentage String semicolon Line 83. Property room As percentage String semicolon Line 84. Property has T A As University dot Teaching Assistant semicolon Line 85. Index has T A Index On has T A open square bracket Unique close square bracket semicolon Line 86. Foreign Key has T A F K open parentheses has T A close parentheses References University dot Teaching Assistant open parentheses close parentheses semicolon Line 87. Relationship has Teacher As University dot Faculty open square bracket Cardinality equals one comma Inverse equals teaches comma Line 88. Required close square bracket semicolon Line 89. Relationship has Student As University dot Enrollment open square bracket Cardinality equals many comma Inverse equals class Taken close square bracket semicolon Line 90. Relationship is Section Of As University dot Course open square bracket Cardinality equals parent comma Inverse equals Line 91. Has Section comma Required close square bracket semicolon Line 92. Relationship given In As Universit dot Mark open square bracket Cardinality equals many comma Inverse equals given To close square bracket semicolon Line 93. close curly brace Line 94. Class University dot Enrollment Extends percentage Persistent open curly brace Line 95. Relationship student Enrolled As University dot Student open square bracket Cardinality equals one comma Inverse equals Line 96. Takes Class comma Required close square bracket semicolon Line 97. Relationship class Taken As University dot Class Section open square bracket Cardinality equals one comma Inverse equals Line 98. Has Student comma Required close square bracket semicolon Line 99. Index enrolment Index On open parentheses student Enrolled comma class Taken close parentheses open square bracket Unique close square bracket semicolon Line 100. close curly brace Line 101. Class University dot Evaluation Extends open parentheses percentage Persistent close parentheses open curly brace Line 102. Property eval Date As percentage Date open square bracket Required close square bracket semicolon Line 103. Property rater Name As percentage String open square bracket Required close square bracket semicolon Line 104. Property rating As percentage String open parentheses VALUELIST equals double quotes 1 comma 2 comma 3 comma 4 comma 5 double quotes close parentheses open square bracket Required close square bracket semicolon Line 105. Relationship is Eval Of As University dot Faculty open square bracket Cardinality equals parent comma Inverse equals has Evaluation close square bracket semicolon Line 106. Index eval Index On open parentheses eval Date comma is Eval Of close parentheses open square bracket Unique close square bracket semicolon Line 107. close curly brace Line 108. Class University dot Mark Extends open parentheses percentage Persistent close parentheses open curly brace Line 109. Property grade As percentage String open parentheses VALUE LIST equals double quotes A comma B comma C comma D comma F comma W comma I double quotes close parentheses semicolon Line 110. Relationship given Student As University dot Student open square bracket Cardinality equals one comma Inverse equals earned Grade comma Line 111. Required close square bracket semicolon Line 112. Relationship given To As University dot Class Section open square bracket Cardinality equals one comma Inverse equals given In comma Line 113. Required close square bracket semicolon Line 114. Index mark Index On open parentheses given Student comma given To close parentheses open square bracket Unique close square bracket semicolon Line 115. close curly brace

FIGURE 9.8 The University Schema Using Iris

Iris Studio allows designers to create classes whose objects are persistent simply by adding Extends (%Persistent) after the class name. The class Person is defined as persistent, which means that objects of type Person are stored in the database. Person also has an index on pId together with the Unique specification, which defines pId to be a key for the class. The Index and Unique specifications are used to define keys for several other classes. Notice that the keys for Department and Evaluation are composite keys.

Recall in the UML diagram of Figure 9.5 that Faculty and Student are subclasses of Person. In Iris, this subclass relationship is indicated by the phrase Extends University.Person on the class definition line. Because Person is defined to be a persistent class, Faculty and Student are also persistent. The same is true for Undergraduate and Graduate, which are defined as Extends University.Student and TeachingAssistant, which is defined as Extends University.Graduate.

Note that rank in Faculty has a list of possible values, and in Student there is an initial value for credits and a range for gpa. In general, Iris provides several features for enhancing the definition of attributes, such as length specifications for String types as shown in the Address class, as well as formatting for values like phone numbers and social security numbers.

When creating a persistent class in Iris, the term property is used to refer to both attributes and relationships. The resulting class definition, however, makes a distinction between properties as attributes and properties as relationships, as in the ODL of the ODMG model. Relationships can be one-to-many or parent-to-child. The advises relationship in Faculty provides an example of a one-to-many relationship, where advises is composed of many objects from the Student class. The inverse is the hasAdvisor relationship in the Student class. As defined in the Student class, hasAdvisor points to only one Faculty object and specifies that the inverse is the advises relationship in the Faculty class.

Parent-to-child relationships are one-to-many specifications indicating that dependencies exist. For example, the hasSection relationship of Course defines the cardinality as children, meaning that a course has many sections and the sections are existence dependent on the course. Likewise, the isSectionOf relationship in ClassSection is defined with a cardinality of parent, meaning that a class section is related to one course and is existence dependent on the course. This definition is consistent with the UML relationship definition between Course and ClassSection in Figure 9.5.

In Iris, one-to-one relationships are not explicitly represented using inverse relationship definitions. Instead, a one-to-one relationship is defined as a property, where one class points to objects of a second class as the property value. To enforce the one-to-one semantics, a unique index can be defined on the property. A foreign key definition can also be used to maintain referential integrity. As an example, the UML diagram in Figure 9.5 defines a one-to-one relationship between Department and Faculty with respect to the chair of the department: a department has one chair and a faculty member can only chair one department. In the Iris class definition of Department in Figure 9.8, hasChair is defined as a property with a value of type Faculty. The Faculty class has no such inverse property definition. The Department class, however, defines a Unique index on the hasChair property to create the intended one-to-one semantics

Line 1. Property has Chair As University dot Faculty semicolon. Line 2. Index has Chair Index On has Chair open square bracket Unique close square bracket semicolon.

The Unique index will prevent a faculty object from being assigned as a chair to more than one department. A foreign key is also defined to ensure referential integrity with respect to faculty objects

Foreign Key has Chair F K open parentheses has Chair close parentheses References University dot Faculty open parentheses close parentheses semicolon.

The hasChairFK foreign key definition in Iris provides the same functionality as it does in the relational model, indicating that a faculty object cannot be deleted if it is also referenced as the chair of a department.

When mapping one-to-one relationships from a UML diagram to an Iris schema, it is a design decision as to which side of the relationship to use to define the property. In general, the property should be placed on the side where the most queries will occur about the relationship. In the one-to-one relationship between Department and Faculty, a department always has a chair. In the opposite direction, most faculty members do not serve as department chairs. As a result, it is a better design decision to define the property in the Department class. The name of the department chair can easily be retrieved with SQL in Iris using an implicit join of the relationship, which is the same as dot notation in OQL, with the dot replaced by an arrow notation. As an example, the following query retrieves the department name and the first and last name of the chair of the computer science department

Line 1. SELECT d dot dept Name comma d dot has Chair right arrow f Name comma d dot has Chair right arrow l Name. Line 2. FROM Department d. Line 3. WHERE d dot dept Name equals single quote Computer Science single quote semicolon.

The other one-to-one relationship in the UML diagram of Figure 9.5 is the relationship between ClassSection and TeachingAssistant. In this case, ClassSection defines hasTA as a property with a type of TeachingAssistant, including the appropriate unique index and foreign key definitions.

Iris does not directly support many-to-many relationships, such as the many-to-many hasPrerequisite/isPreReqOf relationships of the Course class in Figure 9.5. To represent this many-to-many relationship, the Prereqs association class is defined. A Course then represents its prerequisites through a one-to-many hasPreReq relationship to instances of the Prereqs class. Each instance of the Prereqs class has the many-to-one relationship isPreReq, which then points back to the class instance that is the prerequisite. From the Course class, the relationships can be traced backwards to identify the courses for which a course is a prerequisite. For example, from Course, hasPreReq finds the Prereqs instances, which then point to courses through the isPreReqOf relationship. Notice that the PreReqs class creates a composite key (isPreReqOf, isPreReq) for objects in the class through the definition of a unique index. In a similar manner, the Enrollment association class is used in Figure 9.8 to represent the many-to-many relationship between students and the class sections in which they enroll. The Mark class is also created to record the grade that each student earns in the classes that they complete. This relationship was represented in the UML diagram in Figure 9.5 as a many-to-many relationship between Student and ClassSection, with grade as an attribute of the relationship.

..................Content has been hidden....................

You can't read the all page of ebook, please click here login for view all page.
Reset
3.144.230.172