Object-Role Modeling (ORM/NIAM)

Terry Halpin

Microsoft Corporation, USA

 

Introduction

1.1 ORM: what is it and why use it?

Object-Role Modeling (ORM) is primarily a method for modeling and querying an information system at the conceptual level. In Europe, the method... often... (call) NIAM (Natural language Information Analysis Method). Since information systems... typically... (implement) on a DBMS that is based on some logicaldata model (e.g. relational, object-relational, hierarchic), ORM... (include) procedures for mapping betweenconceptual and logical levels. Although various ORM extensions... (propose) for process and eventmodeling, the focus of ORM is on data modeling, since the data perspective is the most stable and it... (provide) a formal foundation on which operations can be defined.

For correctness, clarity and adaptability, information systems... best... (specify) first at theconceptual level, using concepts and language that people can readily understand. Analysis and design... (involve) building a formal model of the application area or universe of discourse (UoD). To do this properly... (require) a good understanding of the UoD and a means of specifying this understanding in a clear,unambiguous way. Object-Role Modeling... (simplify) this process by using natural language, as well asintuitive diagrams that can be populated with examples, and by expressing the information in terms ofelementary relationships.

ORM... (so-call) because it pictures the world in terms of objects (entities or values) that play roles (parts in relationships). For example, you are now playing the role of reading, and this paper is playing therole of being read. In contrast to other modeling techniques such as Entity-Relationship (ER) and Object-Oriented (OO) approaches, ORM makes no explicit use of attributes. For example, instead of usingcountryBornas an attribute of Person, we... (use) the relationship type Person was born in Country. This... (have) manyimportant advantages. Firstly, ORM models and queries are more stable (attributes may evolve into entitiesor relationships). For example, if we decide to later record the population of a country, then our countryBornattribute needs to be reformulated as a relationship. Secondly, ORM models may... conveniently... (populate) with multiple instances (attributes make this too awkward). Thirdly, ORM is more uniform (e.g. we don’tneed a separate notation for applying the same constraint to an attribute rather than a relationship).

ORM is typically more expressive than ER or OO. Its role-based notation makes it easy to specify awide variety of constraints, and its object types... (reveal) the semantic domains that bind a schema together.One benefit of this is that conceptual queries may now... (formulate) in terms of schema paths, wheremoving from one role though an object type to another role amounts to a conceptual join (see later).

Unlike ORM or ER, popular OO models often... (duplicate) information by wrapping facts up into pairsof inverse attributes in different objects. Moreover, OO notations have weak support for constraints (e.g. aconstraint might have to be duplicated in different objects, or even ignored). Unfortunately, OO models are less stable than even ER models when the UoD... (evolve). For such reasons, OO models should  ... (use) onlyfor implementation, not for analysis.

Although the detailed picture provided by ORM is desirable in developing and transforming amodel, for summary purposes it is useful to hide or compress the display of much of this detail. Variousabstraction mechanisms... (exist) for doing this [e.g. CHP96]. If desired, ER and OO diagrams can also  ... (use) for providing compact summaries, and  ... best... (develop) as views of ORM diagrams. For a simplediscussion illustrating the points in this section, see [Hal96].

The rest of this article... (provide) a brief history of ORM, summarizes the ORM notation,... (illustrate) the conceptual design and relational mapping procedures, and  ... (mention) some recent extensions beforeconcluding.

 

Exercise 3.2. Underline the link words that are used in the paper.

Exercise 3.3. Put the link words into the correct column of the table below.

Reason	Contrast	Listing points	Positive addition	Example

 

Exercise 3.4. Fill in the prepositions of(2) on (2) to in to make word combinations complete.

1. the focus of ORM is … data modeling

2. in contrast … other modeling techniques

3. expressing the information … terms … elementary relationships

4. based … some logical data model

5. instead … using countryBornas an attribute of Person

Exercise 3.5. Make up your own sentences using the word combinations given inEx. 3.4.

Exercise3.6. Summarize the Introduction.

Exercise3.7. Boost your vocabulary with the words from the Introduction.

Noun	Verb	Adjective	Adverb
query	implement	hierarchic	conveniently
adaptability	propose	conceptual	primarily
variety	specify	compact
constraint	evolve	unambiguous
path	reveal	awkward
	simplify	explicit
	conclude	separate
	populate	desirable
	map	various
	bind	recent

 

PART B

Exercise3.8. Read and analyze the Introduction given below.