Introduction to Geodatabase(gdb), Type of Geodatabase and there differences.

Introduction to Geodatabase(gdb), Type of Geodatabase and there differences.

A geodatabase is an alternate way to store GIS information in one large file, which can contain multiple point, polygon, and/or polyline layers. ESRI is pushing the geodatabase idea, because it is a less “messy” way of organizing data than having multiple shapefiles. in multiple folders. While shapefiles are still very popular and commonly available, you may run into geodatabases in your search for useful data.

At its most basic level, an ArcGIS geodatabase is a collection of geographic datasets of various types held in a common file system folder, a Microsoft Access database, or a multiuser relational DBMS (such as Oracle, Microsoft SQL Server, PostgreSQL, Informix, or IBM DB2). Geodatabases come in many sizes, have varying numbers of users and can scale from small, single-user databases built on files up to larger workgroup, department, and enterprise geodatabases accessed by many users.

But a geodatabase is more than a collection of datasets; the term geodatabase has multiple meanings in ArcGIS:

• The geodatabase is the native data structure for ArcGIS and is the primary data format used for editing and data management. While ArcGIS works with geographic information in numerous geographic information system (GIS) file formats, it is designed to work with and leverage the capabilities of the geodatabase.
• It is the physical store of geographic information, primarily using a database management system (DBMS) or file system. You can access and work with this physical instance of your collection of datasets either through ArcGIS or through a database management system using SQL.
• Geodatabases have a comprehensive information model for representing and managing geographic information. This comprehensive information model is implemented as a series of tables holding feature classes, raster datasets, and attributes. In addition, advanced GIS data objects add GIS behavior; rules for managing spatial integrity; and tools for working with numerous spatial relationships of the core features, rasters, and attributes.
• Geodatabase software logic provides the common application logic used throughout ArcGIS for accessing and working with all geographic data in a variety of files and formats. This supports working with the geodatabase, and it includes working with shapefiles, computer-aided drafting (CAD) files, triangulated irregular networks (TINs), grids, CAD data, imagery, Geography Markup Language (GML) files, and numerous other GIS data sources.
• Geodatabases have a transaction model for managing GIS data workflows.

Each of these aspects of the geodatabase is described in more detail in the other topics in this section of the help.

Type of Geodatabase:

The geodatabase is a "container" used to hold a collection of datasets. There are three types:

1. File geodatabases—Stored as folders in a file system. Each dataset is held as a file that can scale up to 1 TB in size. The file geodatabase is recommended over personal geodatabases.
2. Personal geodatabases—All datasets are stored within a Microsoft Access data file, which is limited in size to 2 GB.
3. Enterprise geodatabases—Also known as multiuser geodatabases, they can be unlimited in size and numbers of users. Stored in a relational database using Oracle, Microsoft SQL Server, IBM DB2, IBM Informix, or PostgreSQL.
   

 

File geodatabases and personal geodatabases

File and personal geodatabases, which are freely available to all users of ArcGIS Desktop Basic, Desktop Standard, and Desktop Advanced, are designed to support the full information model of the geodatabase, which comprises topologies, raster catalogs, network datasets, terrain datasets, address locators, and so on. File and personal geodatabases are designed to be edited by a single user and do not support geodatabase versioning. With a file geodatabase, it is possible to have more than one editor at the same time provided they are editing in different feature datasets, stand-alone feature classes, or tables.

The file geodatabase was a new geodatabase type released in ArcGIS 9.2. Its goals are to do the following:

• Provide a widely available, simple, and scalable geodatabase solution for all users.
• Provide a portable geodatabase that works across operating systems.
• Scale up to handle very large datasets.
• Provide excellent performance and scalability, for example, to support individual datasets containing well over 300 million features and datasets that can scale beyond 500 GB per file with very fast performance.
• Use an efficient data structure that is optimized for performance and storage. File geodatabases use about one-third of the feature geometry storage required by shapefiles and personal geodatabases. File geodatabases also allow users to compress vector data to a read-only format to reduce storage requirements even further.
• Outperform shapefiles for operations involving attributes and scale the data size limits way beyond shapefile limits.

Personal geodatabases have been used in ArcGIS since their initial release in version 8.0 and have used the Microsoft Access data file structure (the .mdb file). They support geodatabases that are limited in size to 2 GB or less. However, the effective database size is smaller, somewhere between 250 and 500 MB, before the database performance starts to slow down. Personal geodatabases are also only supported on the Microsoft Windows operating system. Users like the table operations they can perform using Microsoft Access on personal geodatabases. Many users really like the text-handling capabilities in Microsoft Access for working with attribute values.

ArcGIS will continue to support personal geodatabases for numerous purposes. However, in most cases, Esri recommends using file geodatabases for their scalability in size, significantly faster performance, and cross-platform use. The file geodatabase is ideal for working with file-based datasets for GIS projects, personal use, and in small workgroups. It has strong performance and scales well to hold extremely large data volumes without requiring the use of a DBMS. Plus, it is portable across operating systems.

Typically, users will employ multiple file or personal geodatabases for their data collections and access these simultaneously for their GIS work.

Enterprise geodatabases

When you need a large, multiuser geodatabase that can be edited and used simultaneously by many users, the enterprise geodatabase provides a good solution. It adds the ability to manage a shared, multiuser geodatabase as well as support for a number of critical version-based GIS workflows. The ability to leverage your organization's enterprise relational databases is a key advantage of the enterprise geodatabase.

Enterprise geodatabases work with a variety of DBMS storage models (IBM DB2, Informix, Oracle, PostgreSQL, and SQL Server). Enterprise geodatabases are primarily used in a wide range of individual, workgroup, department, and enterprise settings. They take full advantage of underlying DBMS architectures to support the following:

• Extremely large, continuous GIS databases
• Many simultaneous users
• Long transactions and versioned workflows
• Relational database support for GIS data management (providing the benefits of a relational database for scalability, reliability, security, backup, integrity, and so forth)
• SQL types for Spatial in all supported DBMSs (Oracle, SQL Server, PostgreSQL, Informix, and DB2)
• High performance that can scale to a very large number of users

Through many large geodatabase implementations, it has been found that DBMSs are efficient at moving in and out of tables the type of large binary objects required for GIS data. In addition, GIS database sizes can be much larger and the number of supported users greater than with file-based GIS datasets.

For information about the enterprise geodatabase architecture and how enterprise geodatabases leverage relational database technology, see Architecture of the geodatabase.