Western Governors University DATABASE 0047relational_databases_unit_5_milestone_5. UNIT 5 — MILESTON

Score 12/17

You passed this Milestone 12 questions were answered correctly.

5 questions were answered incorrectly.

1 What would be a reason why we may want to denormalize our database?

We may want to store pre-aggregated or derived data.

We want to reduce redundancy.

UNIT 5 — MILESTONE 5 We want to eliminate repeating groups.

We want to remove multivalued dependencies.

RATIONALE We may want to denormalize data to avoid extra join conditions to help prioritize performance and reduce input/output operations in the database. There are also cases in which it may be impossible to generate the data required by a report using plain SQL so we may use this approach to allow users to query exactly what the report would look like. The more joins we have, the slower the processing can be. In some cases, having pre-aggregated data or derived data may be important as it may be something that is constantly calculated.

CONCEPT Denormalization 2 Is this dataset in 3NF or not? If not why not?

Yes, it is in 3NF.

No, it is not yet in 2NF.

No, there are repeating groups.

No, there is an issue with the functional dependency.

RATIONALE The first normal form indicates that each cell of a table should contain exactly one value with no repeating groups. The second normal form indicates that the table should already be in first normal form and the primary key of a table should be composed of a single column. No non-prime attribute is dependent on the proper subset of any candidate key of a table. The third normal form indicates that the table should be in second normal form and that there shouldn't be any functional dependency. In 3NF, all transitive functional dependency of a non-prime attribute on any super key should be removed.

CONCEPT Third Normal Form 3 What is a key feature of fourth normal form?

It should be in BCNF to start with.

4NF is also focused on full functional dependency.

4NF is all about join dependencies.

This normal form has the tables broken down into as many tables as possible to avoid redundancy.

RATIONALE A relation will be in 4NF if it is already in BCNF and there are no multi-valued dependencies. There should be a minimum of three columns in which at least two attributes depend on the third one. Those two attributes should be independent of each other.

CONCEPT Higher Normalization 4 In each milestone, you may want or need to use the database and query tool to answer some of the questions. We suggest you open the tool in another browser tab while you are working on this assessment. https://postgres.sophia.org/ What type of cardinality is demonstrated by the following ERD?

A department has a professor. A professor is part of multiple departments.

A department has a professor. A professor is part of a department.

A department has multiple professors. A professor is part of multiple departments.

A department has multiple professors. A professor is part of a department.

RATIONALE If the cardinality is one-to-one, there should be a singular link between both entities. If the cardinality is a one to many, the side with the 1 should have a singular link while the side with the many should have multiple items. If the cardinality is many-to-many, there should be multiple links between both entities.

CONCEPT Relationships and Cardinality 5

What would need to be done to fix an issue with a chasm trap?

Create a foreign key for each primary key in the relationships.

Remove the middle table and connect the tables directly.

The entire database design needs to be re-evaluated.

Create a direct link between the two tables rather than depend on the middle relationship.

RATIONALE To resolve a chasm trap, we need to create a direct table between the two tables that have a relationship rather than depend on the middle relationship to link them together.

CONCEPT ERD Connection Traps 6 In each milestone, you may want or need to use the database and query tool to answer some of the questions. We suggest you open the tool in another browser tab while you are working on this assessment. https://postgres.sophia.org/ What is wrong with the following ERD meant to show the attributes of an entity?

The attributes are not correctly linked to the entity.

The symbols used are swapped.

The primary key is not indicated correctly.

There is nothing wrong with the ERD.

RATIONALE Entities should have rectangles to indicate the entities. Attributes have ovals to distinguish them. To show a relationship between entities and attributes a line is drawn between them. Primary keys should be underlined.

CONCEPT Adding Attributes 7 Identify the normal form in which all of the attributes are set up to be dependent on the primary key.

1NF

None of the first 3 normal forms

2NF

3NF

RATIONALE In 1NF, we use a table format, have no repeating groups, all of the key attributes are defined, have the primary key identified, and have the attributes being dependent on the primary key. In 2NF, we have it in 1NF and have no partial dependencies. In 3NF, we have it in 2NF and have no transitive dependencies. In 4NF, we have it in 3NF and have no independent multivalued dependencies.

CONCEPT Normal Forms 8 In each milestone, you may want or need to use the database and query tool to answer some of the questions. We suggest you open the tool in another browser tab while you are working on this assessment. https://postgres.sophia.org/ What is wrong with the following ERD meant to show a relationship between two entities?

There is no relationship between the entities.

There is nothing wrong with the ERD.

Both of the objects are attributes.

One of the items is set up as an attribute.

RATIONALE Entities should have rectangles to indicate the entities. Attributes have ovals to distinguish them. To show a relationship between entities and attributes a line is drawn between them.

CONCEPT Tables as Entities 9 Is this dataset in 1NF or not? If not, why not?

There are repeating groups with the actor_names and possibly the genre_names.

This data set is in 1NF already.

There are no foreign keys.

There is no primary key.

RATIONALE The first normal form indicates that each cell of a table should contain exactly one value with no repeating groups. The second normal form indicates that the table should already be in first normal form and the primary key of a table should be composed of a single column. No non-prime attribute is dependent on the proper subset of any candidate key of a table. The third normal form indicates that the table should be in second normal form and that there shouldn't be any functional dependency. In 3NF, all transitive functional dependency of a non-prime attribute on any super key should be removed.

CONCEPT First Normal Form 10 What is true about normalization?

Prioritize performance rather than data anomalies.

Store pre-aggregated or derived data.

Our database may not need to have data be inserted, updated, or deleted.

You need to take into account business rules and data constraints.

RATIONALE The main goals of normalization would be to eliminate unnecessary data redundancies and reduce the chance of data anomalies.

Normalization takes existing data structures, defines the business rules, data constraints, and improves the structure of the database.

Through the identification of functional dependencies, entities, and attributes, you can then perform normalization in a series of steps.

CONCEPT Normalization Overview 11 What is a benefit of using a lookup table?

There is data modification flexibility.

They resolve weak entities.

They guarantee that there will be no data redundancies due to functional dependencies.

They transform an M:N relationship into two 1:M relationships.

RATIONALE Lookup tables hold data in the form of key-value pairs. The keys themselves usually are integers or short strings. These keys are used in other tables as foreign keys. There is the benefit of storage savings, performance enhancement for some queries, data centralization, data modification flexibility, and provide quick answers for some questions related to the key-value pairs.

CONCEPT Reference Tables 12 What is a disadvantage of reducing the complexity of data models?

Faster application development

Decreased redundancy

Simpler application code

Simpler queries

RATIONALE When reducing the complexity of the data models, we can have faster application development as you do not have to worry about touching each table. This creates simpler application code to maintain and simpler SQL queries. However, by reducing the complexity, we may not be able to easily adapt for scalability, especially if business rules change as well as increase redundancy.

CONCEPT ERD Example: Complexity 13 In each milestone, you may want or need to use the database and query tool to answer some of the questions. We suggest you open the tool in another browser tab while you are working on this assessment. https://postgres.sophia.org/ What is used to indicate a weak relationship in an ERD?

Double diamond

Dotted line between entities

Single dotted diamond

Single diamond

RATIONALE In an ERD, a weak entity is represented with a double rectangular box with the weak identifying relationship with a double diamond.

CONCEPT Weak Relationships and Entities 14 Is this dataset in 2NF or not? If not, why not?

No, there are repeating groups.

No, there are no transitive functional dependencies.

It is already in 2NF

No, there are columns that are not dependent on the primary key.

RATIONALE The first normal form indicates that each cell of a table should contain exactly one value with no repeating groups. The second normal form indicates that the table should already be in first normal form and the primary key of a table should be composed of a single column. No non-prime attribute is dependent on the proper subset of any candidate key of a table. The third normal form

indicates that the table should be in second normal form and that there shouldn't be any functional dependency. In 3NF, all transitive functional dependency of a non-prime attribute on any super key should be removed.

CONCEPT Second Normal Form 15 Review the sample movie ratings initial data set after 3NF. What is the relationship between table Movie and Rating?

0:1

1:1

1:M

M:N

RATIONALE With the relationship of a Movie and Rating, a movie has many ratings while a rating can only be for a single movie. As such, the relationship between the two is a one-to-many relationship.

CONCEPT ERD Example: Movie Ratings 16 Review the sample eCommerce ERD after 3NF. Which tables are lookup tables?

Category

Customer, Category

PhoneType, AddressType

Category, AddressType, PhoneType

RATIONALE The lookup tables that exist after 3NF include the Category, AddressType, and PhoneType tables. The data in those tables would only be inserted into and not change on a regular basis.

CONCEPT ERD Example: eCommerce 17 What type of key can be used in an associative entity?

No key is needed with an associative entity.

A natural primary key is generally used.

A surrogate key is used.

An artificial primary key is used.

CONCEPT Associative Entities

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