MBA 664 Database Management

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Advancement of the E-R Model. Fundamental E-R Modelnearly 25 years oldcomplex information connections and new database innovation have outgrown it in some respectsEnhanced E-R Modela reaction to the deficiencies of the essential E-R modelnot generally settled upon in some respectsintroduced the supertype/subtype relationship.

Presentation Transcript

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MBA 664 Database Management Dave Salisbury salisbury@udayton.edu (email) http://www.davesalisbury.com/(site)

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Evolution of the E-R Model Basic E-R Model about 25 years of age complex information connections and new database innovation have outgrown it in a few regards Enhanced E-R Model a reaction to the weaknesses of the essential E-R demonstrate not generally settled upon in a few regards presented the supertype/subtype relationship

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Supertype/Subtype Relationships Supertype (illustration: Employee) a non specific substance that has an association with at least one subtypes Subtype (case: Manager) a subgrouping of a supertype element that is significant to an association shares all traits of its supertype, additionally has exceptional characteristics of its own as well as : has associations with different elements unmistakable from those of different subtypes

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Supertype/Subtype Notation

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The understudy case STUDENT UNDERGRAD STUDENT GRAD STUDENT

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Two Rules for When to Use Supertype/Subtypes Use this sort of relationship when either (or both) of the accompanying are available: When there are ascribes that apply to a few (yet not all) of the occasions of an element sort When the cases of a subtype take an interest in a relationship remarkable to that subtype

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Attribute Inheritance "The property by which subtype elements acquire estimations of all properties of the supertype. This essential property makes it pointless to incorporate supertype traits repetitively with the subtypes."

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Name City/State/Zip SSN EMPLOYEE Telephone HOURLY EMPLOYEE SALARIED EMPLOYEE CONSULTANT Annual_Salary Stock_Option Contract_Number Billing_Rate Hourly_Rate Supertype/Subtype Example 1

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Supertype/Subtype Relationships in a Hospital

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Generalization The way toward characterizing a more broad element sort from an arrangement of more particular substance sorts A "base up" approach Specialization The way toward characterizing at least one subtypes of a general element in light of recognizing attri-butes or connections A "beat down" approach Two Processes to Develop Supertype/Subtypes Both methodologies can be utilized together

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Completeness Addresses the subject of whether an occurrence of a supertype should likewise be an individual from no less than one subtype Disjointness Addresses the topic of whether a case of a supertype may all the while be an individual from (at least two) subtypes Supertype/Subtype Constraints

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Completeness Constraint: Two Possible Rules Total Specialization Rule (Double-Line) Specifies that every element occasion of the supertype must be an individual from some subtype in the relationship (Example: all STUDENTS are either UNDERGRADUATE or GRADUATE understudies) Partial Specialization Rule (Single-line) Specifies that an element case of the supertype is permitted to not have a place with any subtype (Example: FACULTY and STAFF are by all account not the only conceivable individuals from the element EMPLOYEE)

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Completeness requirement Total specialization Partial specialization

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Can an element case at the same time be an individual from at least two subtypes? Disconnected requirement Disjoint manage Overlap lead

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Subtype discriminators Attribute of the supertype whose esteem decides to which subtype an occasion has a place

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What does that resemble?

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Yet another illustration… .

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Arrangement of super-and subtypes where each subtype has just a single supertype. Supertype/subtype order

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Another case...

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