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sql allow their implementation using various sql commands

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2012-05-27 08:10:30
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Q: How does SQL allow implementation of entity and integrity constraints?
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How does SQL allow implementation of the entity integrity and referencial integrity constraints what about general integrity constraints?

sql allow their implementation using various sql commands

What are the advantages and disadvantages of Entity Relationship Diagrams?

Entity-Relationship diagrams are useful for modelling data and the relationships between the data. They can be used when the constraints between data are relatively simple. They do not allow specification of interactions between the data or model how the data changes (there are no processes in Entity-Relationship). Entity-Relationship diagrams are most often used to model databases.

What is superkey?

it is a set one or more attribute,that taken collectively allow as to idendify uniquly and entity in entity set. ex-customer-id,

What does a database expert mean when she says that a databse displays both entity and referential integrity?

Entity integrity, also known as a check constraint, is a database imposed restriction that the value of a field be limited. For instance, you could say that a number can only be in the range of 1 to 100, and the database would not allow you to insert or modify a row to have a value outside that range.Referential integrity, also known as a foreign key constraint, is a database imposed restriction that the value of a field be contained in the primary key or a unique key associated with another table. For instance, you could say that a programmer's name be contained in a table of employees, and the database would not allow you to insert or modify a row to have a programmer that is not also an employee. In this example, to clarify, the employee table would contain people that are programmers, as well as analysts, managers, officers, etc.

Why are criteria and constraints important to a design?

it is the limits and necessity of the designs that allow it to function correctly and provid ethe consumer with a pleased design

What was the purpose of a trade unoin?

To allow workers to collectively mobilize, assume unity in bargaining, and preserve the integrity of a trade.

What do you mean by entity and bundle in drupal?

It is better to explain concepts of entity type, bundle, field and entity rather than only entity and bundle. Entity Type: An entity type is a useful abstraction to group together fields. Let's consider some examples of entity types: • Nodes • Comments • Taxonomy terms • User profiles Bundle: Bundles are an implementation of an entity type to which fields can be attached. You can consider bundles as subtypes of an entity type. With content nodes, for example, you can generate bundles like articles, blog posts, or products. Not all entity types have bundles, however. For example, users do not have separate bundles. For the entity types that do allow bundles, you can create as many bundles as you want. Then, using the Field system, you can add different fields to each bundle. Examples include a file download field on Basic Pages and a subtitle field on Articles Field: A field is a reusable piece of content. In technical terms, each field is a primitive data type, with custom validators and widgets for editing and formatters for display. What's important to know as it relates to Entities is that Fields can be added to any of the bundles to help organize their data. Entity: An entity would be one instance of a particular entity type such as a comment, taxonomy term or user profile or a bundle such as a blog post, article or product.

Two principal integrity rules for the relational model?

Integrity Rules Although integrity rules are not part of normal forms, they are definitely part of the database design process. Integrity rules are broken into two categories. They include overall integrity rules and database-specific integrity rules. == The two types of overall integrity rules are referential integrity rules and entity integrity rules. Referential integrity rules dictate that a database does not contain orphan foreign key values. This means thatEntity integrity dictates that the primary key value cannot be Null. This rule applies not only to single-column primary keys, but also to multi-column primary keys. In fact, in a multi-column primary key, no field in the primary key can be Null. This makes sense because, if any part of the primary key can be Null, the primary key can no longer act as a unique identifier for the row. Fortunately, the Access Database Engine (Access 2007's new version of the JET database engine, available with the new ACCDB file format) does not allow a field in a primary key to be Null.Database-Specific Rules The other set of rules applied to a database are not applicable to all databases but are, instead, dictated by business rules that apply to a specific application. Database-specific rules are as important as overall integrity rules. They ensure that only valid data is entered into a database. An example of a database-specific integrity rule is that the delivery date for an order must fall after the order date.

What is key constraints?

Primary Key is a Constraint Used to avoid Duplicate entries in database table and you define primary key the column doesn't allow NULL values.

Is the US-Government considered a business?

No. A business is fundamentally a "for profit" entity. The US Govt can engage in transactions with businesses, and can even allow itself to be sued as a result of those transactions. However, the US Government is wholly different sort of entity.

Can you call a virtual function from a constructor?

Yes. Any method inherited through virtual inheritance is visible to the entire class, including its constructors. This includes virtual and pure-virtual methods. However, unless called explicitly, the most-derived implementation of the virtual function will be called. Explicit calls allow a derived class's implementation to call its base class implementation.

What is the definition of 'entity' in xml?

XML entities allow you to use text to refer to a data item, instead of using the data item itself. There are 5 predefined entity references in XML. These are:Entity ReferenceCharacter<<>>&&""''

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