Table Basics [转载]

In the geodatabase, attributes are managed in tables based on a series of simple yet essential relational data concepts:

• Tables contain rows.
• All rows in a table have the same columns.
• Each column has a data type, such as integer, decimal number, character, and date.
• A series of relational functions and operators (such as SQL) is available to operate on the tables and their data elements.

 

Tables and relationships play a key role in ArcGIS, just as they do in traditional database applications. Rows in tables can be used to store all the properties of geographic objects. This includes holding and managing feature geometry in a Shape column.
The illustration below shows two tables and how their records can be related to one another using a common field.

 

Attribute data types in the geodatabase

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 There are a number of supported column types used to hold and manage attributes in the geodatabase. The available column types include a variety of number types, text, date, binary large objects (BLOBs), and globally unique identifiers (GUIDs). 

The supported attribute column types in the geodatabase include

• Numbers: Can be one of four numeric data types: short integers, long integers, single-precision floating-point numbers (often referred to as floats), and double-precision floating-point numbers (commonly called doubles). 
• Text: Any set of alphanumeric characters of a certain length.
• Date: Holds date and time data.
• BLOBs: Binary large objects used to store and manage binary information such as symbols and CAD geometries.
• Global Identifiers: GlobalID and GUID data types store registry style strings consisting of 36 characters enclosed in curly brackets. These strings uniquely identify a feature or table row within a geodatabase and across geodatabases. These are heavily used to manage relationships, especially for data management, versioning, change-only updates, and replication.

XML column types are also supported through programming interfaces. The XML column can hold any formatted XML content (such as metadata XML).
See Geodatabase field data types for more information.

Extending tables

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 Tables provide descriptive information for features, rasters, and traditional attribute tables in the geodatabase. Users perform many traditional tabular and relational operations using tables. 

In the geodatabase, there is a focused set of capabilities that are optionally used to extend the capabilities of tables. These include the following:

Working with attribute tables in the geodatabase

Use these	If you need to
Attribute Domains	Specify a list of valid values or a range of valid values for attribute columns.  Use domains to help ensure the integrity of attribute values.  Domains are often used to enforce data classifications (such as road class, zoning codes, and land use classifications).
Relationship Classes	Build relationships between two tables using a common key.  Find the related rows in a second table based on rows selected in the original.
Subtypes	Manage a set of attribute subclasses in a single table.  This is often used on feature class tables to manage different behaviors on subsets of the same feature types.
Versioning	Manage long update transactions, historical archives, and multiuser editing required in GIS workflows.