13th International Conference on the Entity-Relationship Approach, An EER schema can be depicted with graphical notations (diagrams): entity- types are relationships are diamond shaped boxes; aggregates are depicted by boxes with dotted in  which the interested reader can refer to for more detailed comments. 13d or Fig. Entity-Relationship Technique—Relational Database The idea in this case will be to between garages and mechanics is represented in the entity-relationship diagram of Fig. 14 by the diamond-shaped box connecting them. In an E-R diagram relationship is represented by. (a) circles. (b) rectangles . (c) diamond shaped box. (d) ellipse. Entities are identified from the.
Arrays are passed as arguments to a function by a value b reference c both a and b d none of the above A data structure in which elements are added and removed from only one end, is known as: A diamond-shaped box in an Entity-Relationship diagram refers to: The principle means of identifying entities within an entity set is: C language is available for which of the following Operating Systems?
Which of the following have the fastest access time? Array subscripts in C always start at: Which type of commands in DOS needs additional files for their execution?
Which of the following statements in regard to Directories is false? It is better to buffer a table when a When a table is read infrequently b When a table is linked to check tables c When a table is read frequently and the data seldom changes d When a single record is to be picked up The Operating System is responsible for: A company whishes to connect two sites in different parts of the country together. It is decided to use the telephone system. What device should be connected to the fileservers on each site?
What is a file server?
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What is the Protocol used for the Internet? Which one of the following is not a Normal Forms Normalization rule with regards to the Relational Model?
Choose the answer which best describes the term Primary Key: Which technique is used to reduce the size of a file: A floppy disk is consisting of 40 tracks, each track contains sectors, and the capacity of a sector is bytes, what is the approx. What is the binary equivalent of a decimal number Comes about when an instance of the superentity type must always have one and only one subtype counterpart; therefore, the potential subtype occurrences in question are mutually exclusive.
This is the kind that concerns to your scenario. A typical case in which an exclusive supertype-subtype comes about is a business domain where both an Organization and a Person are considered Legal Parties, like in the situation deliberated in this series of posts.
Presents itself when a supertype instance may be complemented by multiple subtype occurrences, each of which is compelled to be of a different category.
An example of this kind of supertype-subtype is dealt with in these posts.
It is worth mentioning that supertype-subtype structures —being elements of a conceptual character— do not belong to a specific data management theoretical framework, be it relational, network or hierarchical —each of which offers particular structures to represent conceptual elements—. It is also opportune to point out that although supertype-subtype clusters bear a certain resemblance to object-oriented application programming OOP inheritance and polymorphism, they are in fact distinct devices because they serve different purposes.
In a database conceptual model —that must represent real world aspects— one deals with structural features in order to describe informational requirements, whereas in OOP polymorphism and inheritance, among other things, one a sketches and b implements computational and behavioural characteristics, aspects that decidedly belong to appplication program design and programming.
In this respect, an application programmer may typically create, e. Using entity-relationship constructs to represent a conceptual model with supertype-subtype structures You asked for an entity-relationship diagram ERD for brevity but, although being an extraordinary modeling platform, the original method —as introduced by Dr. Peter Pin-Shan Chen2— did not supply enough constructs to represent scenarios of the sort being discussed with the precision that a proper database conceptual model requires.
Consequently, it was necessary to make some extensions to said method, situation that yielded results in the development of an approach that assists in the creation of enhanced entity-relationship diagrams EERDs that, naturally, enriched the initial diagramming technique with new expressive characteristics. One of those characteristics is, precisely, the possibility of depicting supertype-subtype structures. Elmasri and Shamkant B.
It is also available as a PDF that can be downloaded from Dropbox. As you can see in the aforementioned diagram, both Group and SoloPerformer are displayed as exclusive subtypes of the Artist superentity type: Discriminator property Also within the scope of the disjointness factor of this supertype-subtype association, it is worth paying close attention to the Artist.
Type property, since it carries out a very relevant task in this arrangement: It is named in this way as it is the property that points out the exclusive kind of subtype with which a specific instance of an Artist relates to. In the cases of nonexclusive clusters, the use of a discriminator property is needless, for a certain supertype can have multiple subtypes as complements as brought up above.
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Total specialization rule and completness The requirement that stipulates that every Artist must always have a supplementary subtype instance has to do with the completness characteristic of this cluster.
This is delineated by means of a total specialization rule, demonstrated via the double-line symbol connecting a the Artist supertype with b the disjoint rule construct. N association or relationshipwhich I represented with the diamond-shaped box labeled as Group-SoloPerformer. If implemented in a relational database as a base table, this component would be very useful to derive i.
Thus, this is another example of a M: