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29 Cards in this Set
- Front
- Back
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What is a database? |
A database is collection of persistent data that models the world as a shared resource. |
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What is a DBMS? |
DBMS(Database management system) is software that is specialized in handling large pieces of data and managing it by providing retrieval and persistence. |
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What is the purpose of a DBMS? |
It handles all the interactions with the database. it provides easy access using a declarative query language. It checks for constraints which saves programmer time. It ensures data independence. it offers concurrent access and automatic recovery from updates. Finally it offers security by restricting access to just specific users. |
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What three levels of abstraction does the database system use to hide details from users? |
the physical level: how the data is stored the logical level: based on a data model the view level: what programs of the user sees. |
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How does the level of abstractions ensure data independence? |
it offers physical data independence, i.e. that the physical level may be changed without affecting the logical level. |
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What is an instance in the context of a database. |
An instance is a collection of data at a given time within the database. |
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What is the schema of a database? |
The schema is the overall design of the database. There are schemas for each level abstraction of the database. schemas at the view level are sometimes called sub schemas. |
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What are disadvantages of using a specific DBMS? |
Your data is locked into one solution. it can be costly to maintain in both space and time. |
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give examples of common end users of DBMS? |
Database administrators, end users, application programmers and enterprise administrator who is responsible for database design. |
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Describe the three parts of a data model |
the structural part: the integrity part: the manipulative part: declarative or procedural. |
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How does the relational model map to the generic datamodel? |
the structural part: relations the integrity part: keys and foreign keys the manipulative part: SQL or query language. |
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Why do we look into the entity relation model? |
It is an example of a highlevel database model. it helps us design before moving to a lower level model. |
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What are alternatives to the entity relation model? |
UML |
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name the components of the structural part of the entity model |
entity types, attributes, relationship types |
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What are the integrity constraints of the entity model? |
primary keys for entity types and relationship types. |
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Why is the ER model only considered a partial data model? |
it has no standard manipulative part. |
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State some advantages of the ER model |
it is relatively simple, it is user friendly and it provides a unified view unlike any implemented data model. |
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what are the main building blocks of the an ERD? |
entities and entity types, relationships and relationship types, attributes, attribute values and domains. |
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Describe and entity. |
an entity is a "thing" that can be uniquely identified. An entity type is a collection of similar entities, which is similar to a class in object oriented languages. |
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what do attributes represent on entities |
they represent properties of entities |
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How are entities represented in an ERD diagram? |
by a rectangle. |
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how are attributes represented in an ERD? |
they are represented by an oval. |
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Can attributes have multiple values in ERDs? |
yes, these are normally represented by a double oval. |
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What is a domain in an ERD diagram? |
a domain of an attribute is the set of constant values that can be associated with an attribute. |
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What is an atomic domain in ERDs? |
integers for instance |
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what is a set valued domain in ERDs? |
finite sets. |
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What are relationship types? |
A relationship type is an association between two or more entities. |
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how are relationship types represented in an ERD? |
using a diamond shape with lines to to each of the entities involved. |
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What is a relationship in an ERD? |
a relationship is an instance of a relationship type, i.e. it is a set of associations between entities. |
