Multiplicity Constraint

Multiplicity Constraint

Multiplicity in entity relationships describes the instances between entities (Rybola & Richta, 2013). This is denoted by indicating a lower and upper limit for a relationship. Entity relationships can be one-to-one, one-to-many, or many-to-many (Connolly & Begg, 2015). For example, a relationship between entities X and Y can have diversity as the number of instances that entity Y can have for a single entity X. The lower and upper number of instances for entity X could be indicated as 0…*. Where 0 would denote zero number of instances and * would denote several instances. When designing a database, the database designer implements an assortment of entity relationships based on the information provided by the client. This is determined by the sample data provided (Connolly & Begg, 2015). Multiplicity constraints can be illustrated on entity relationship diagrams (ERDs) (Rybola & Richta, 2013). ERDs are easier and faster for database professionals to communicate a database’s design than writing a narration.

The private owner and property for-rent entities have their multiplicity illustrated in an ERD (Connolly & Begg, 2015). Both entities have lower and upper limit instances indicated for their relationship. The private owner entity has its multiplicity denoted as 1..1 while the multiplicity for property for rent entity is 1..*. This means that a private owner’s lower and upper limit is 1. The lower limit for property for rent entity is 1, while its upper limit is *. Therefore, one private owner could own one or several properties, and one private owner could own one or several. Another way to describe diversity is where only one owner number can link with one-to-many property numbers. Multiple owner numbers cannot link to the exact property number(s). The owner number is the primary key for the private owner table, and the property number is the primary key for the property for rent table.

References

Connolly, T., & Begg, C. (2015). Database Systems: A Practical Approach to Design, Implementation, and Management (6th ed.). Pearson Higher Ed.

Rybola, Z., & Richta, K. (2013). Possible Realizations of Multiplicity Constraints. Computer Science and Information Systems, 10(4), 1621-1646. https://www.researchgate.net/publication/270471274_Possible_Realizations_of_Multiplicity_Constraints

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Multiplicity Constraint

Instructions

Part A – Complete Review Question 11.4 on page 354 AND explain how you would apply 3 of those techniques if you were asked to collect information regarding improving the learning management system we use in this class.

11.4 A database developer commonly uses several fact-finding techniques during a single database project. The five most widely used techniques are examining documentation, interviewing, observing the business in operation, conducting research, and using questionnaires. Describe each fact-finding technique and identify the advantages and disadvantages of each.

 Part B – Complete Review Question 12.4 on page 383 (you only need to include concepts through section 12.6.3) AND describe the relationship that exists between the Private Owner entity (table) and the PropertyForRent entity (table) in the Dream Home database used in our textbook. (The relevant tables can be found on page 112). HINT – review the Chapter 12 Study Aid (download the document) and the Table Relationships – Multiplicity topic in the Terms and Concepts discussion.

12.4 Describe what the multiplicity constraint represents for a relationship type.

References

Connolly, T. M., & Begg, C. E. (2005). Database systems: a practical approach to design, implementation, and management. Pearson Education.