TechMight Solutions: Entity Relationship Diagram for Music Company
The Music Database project is to categorize and catalog every single piece Schema Users Data Admin Data Artist Data Music Schema Playlist Data Tables In ER- Diagram The Most Important Tables in our project: •Songs. Step 4 - Entity Relationship Diagram. Nikitha Dhanekula. Primary key: of single attribute or multiple attributes in combination. Composer Table. In a database conceptual model —that must represent real world aspects— one deals Music Artists Enhanced Entity-Relationship Diagram.
Print There is no one correct design for the music scenario posed on the last page. The figure below depicts one design. Note the FK notation beside some of the fields.
FK stands for foreign key and indicates a field whose values uniquely identify rows in another table. There is no way to designate a field as a foreign key in MS-Access. For our purposes, you should just remember that building foreign keys into your database is what will enable you to create the table joins needed to answer the questions you envision your database answering. Instructor's homemade entity-relationship diagram for his version of the music album review database design.
If you have questions about this design or see ways to improve it, please share your thoughts in the Lesson 2 Discussion Forum. In this part of the lesson, we'll create and populate some of the tables depicted in the diagram above to give you a sense of how to move from the design phase to the implementation phase of a database project.
Table creation is something that can be accomplished using SQL, as we'll see later in the course. An integral part of creating a table is defining its fields and the types of data that can be stored in those fields. Here is a list of the most commonly used data types available in Access: Among these are Default Value which specifies the value the field takes on by default, and Required, which specifies whether the field is allowed to contain Null values.
It is also possible to specify that a field is the table's primary key or part of a multi-field primary key. Perhaps the most commonly set field property is the Field Size.
For Text fields this property defaults to a value of characters. This property should be set to a lower value when appropriate, for a couple of reasons.
First it will reduce the size of the database, and secondly it can serve as a form of data validation e. When dealing with a Number field, the Field Size property is used to specify the type of number: With this background on fields in mind, let's move on to implementing the music database. Create a new table Open Access and from the opening screen click on the Blank Database icon.
Learning MySQL by Hugh E. Williams, Saied M.M. Tahaghoghi
Every subtype has, in turn, a particular set of properties that are applicable to itself only. Supertype-subtype clusters can be of two kinds: 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.
Entity Relationship Modeling Examples - Learning MySQL [Book]
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.
Music Database | Editable Entity Relationship Diagram Template on Creately
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.Entity Relationship Diagram (ERD) Tutorial - Part 2
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.