GIS data format: Geodatabase

Transferred from: http://www.cnblogs.com/quansixiang/archive/2010/09/17/1829286.html

1 Geodatabase Concept

Geodatabase is a new object-oriented spatial data model introduced by ARCINFO8, which is a unified and intelligent spatial data model based on DBMS. "Unification" means that many spatial data models before geodatabase can not describe the geospatial feature information uniformly under a unified model framework, and Geodatabase does this; "intellectualization" means, in the Geodatabase model, Compared with the former spatial data model, the description and expression of spatial elements are closer to our real world, which can reflect the information of real space objects more clearly and accurately.

The design of Geodatabase is mainly aimed at the extension of standard relational database technology, which expands the traditional point, line and polygon features, and defines a unified model for spatial information. Based on this model, users can define and manipulate specific models of different applications, such as traffic planning model, land management model, power line model and so on. Geodatabase provides a unified, powerful platform for creating and manipulating data models for different users.

Because Geodatabase is an object-oriented data model, in this model, entities in space can be represented as objects with properties, behaviors, and relationships. Geodatabase describes geographic objects mainly in the following four forms:

(1) using vector data to describe discontinuous objects;

(2) Using raster data to describe continuous objects;

(3) Describe the geographical surface with tins;

(4) Use location or address to describe the address.

Geodatabase also supports the expression of objects with different types of characteristics, including simple objects, geographic features (objects with spatial information), network features (objects with geometric relationships to other features), topological-related features, annotation features, and other more specialized feature types. The model also allows the definition of relationships and rules between objects, thus preserving the integrity of the correlation and topology among the object objects.

2 Geodatabase System Structure

Geodatabase organizes geographic data in hierarchical data objects. These data objects are stored in the feature class (Feature Classes), the object class (0bject Classes), and the DataSet (Feature datasets). The Object class can be understood as a table that stores non-spatial data in geodatabase. The Feature class is a collection of features with the same geometry type and attribute structure (Feature).

A feature dataset (Feature datasets) is a collection of common spatial reference feature classes. Feature Class (Feature Class) storage can organize simple features within a feature dataset (Feature datasets) or separate from feature datasets (Feature datasets). A simple feature class (Feature Class) that is independent of the feature dataset (Feature datasets) is called a standalone feature class (Feature Class). Feature classes that store topological features (Feature) must be within a feature dataset (Feature DataSet) to ensure a common spatial reference.

The basic architecture of Geodatabase includes feature datasets, raster datasets, tin datasets, stand-alone object classes, stand-alone feature classes, independent relationship classes, and attribute domains. The feature DataSet is composed of object class, feature class, relationship class and geometric network.

3 Geodatabase of three storage solutions

Geodatabase provides different levels of spatial data storage schemes, which can be divided into three--personalgeodatabase (personal space databases), file Geodatabase (database based on the document format), and ArcSDE Geodatabase (Enterprise-level spatial database).

1. Personal Geodatabase

Personal Geodatabase is mainly applicable to the CIS system which works under single user, and is suitable for the geographic information system of small projects. ArcGIS also has full-featured support for personal geodatabase. Personal Geodatabase is actually a Microsoft Access database that automatically installs Microsoft Jet when users install ArcGIS, and users no longer have to install a Microsoft Access database. That is, Personalgeodatabase is free for ArcGIS users, and it uses data files from Microsoft Jet engine to store spatial data in an Access database. Personal Geodatabase is more like a file-based workspace, it is important to note that Personal Geodatabase has a maximum capacity of 2G and only supports the Windows platform when using Personal geodatabase.

2. File Geodatabase

In the ArcGIS 9.2 release, a new spatial data storage solution,--file Geodatabase, is also available for single-user environments, as well as supporting a complete geodatabase data model, which also allows users to use large datasets without a DBMS. File geodatabase data is stored as files in folders in Windows, Solaris, and Linux systems. In terms of capacity constraints, each table in File Geodatabase can store 1TB of data, which means that users can support very large datasets for any application purpose. The Fiel Geodatabase also has the option of compressing the vector data, which allows the user to reduce the disk footprint while guaranteeing performance, and the compression ratio can reach between 2:1 and 25:1. From the current testing situation, the File Geodatabsse performance is 20% to 10 times times higher than the personal geodatabase. With compression, it has the same performance as the shape file and is stronger than personal geodatabase. When the same data is stored, File geodatabase reduces the disk footprint by 50% to 80% compared to the personal geodatabase.

ArcGIS provides tools to extract a file geodatabase from the geodatabase in the DBMS form and to put a file geodatabase in the human DBMS. Users can easily create file Geodatabaee by loading data from any other geodatabase or supported file structure, such as a shape file. File Geodatabase is easily accessed and used by ArcGIS Desktop, ArcGIS engine, and ArcGIS server.

In addition, File Geodatabage supports storing massive raster datasets that are compatible with the ARCSDE raster schema. From the current trend, File Geodatabase will gradually replace personal geodatabase.

3. ArcSDE Geodatabase

The ArcSDE geodatabase is primarily used in GIS systems that work in multi-user network environments. Through the TCP/IP protocol, ARCSDE, which is installed on the server that manages the relational database of enterprise data, provides ARCSDE geodatabase for CIS applications running on the client. With ARCSDE, users can store a variety of data products in a business database system in accordance with the Geodatabase model, and obtain efficient management and retrieval services.

One of the most important features of ArcSDE Geodatabase is the use of ARCSDE for multi-user parallel operation of spatial data in a networked environment. In addition, the version control mechanism provided by ArcSDE Geodatabaee is also personal geodatabaee and file geodatabase. With ARCSDE, users can access the SDE layer in 0racle, Microsoft SQL Server, Infomix, and DB2.

When users create Geodatabase from the SDE layer, the client needs to add metadata tables to those layers. The metadata includes subclasses, domains, association classes, feature sets, and so on, which enables the ARCSDE-managed spatial database to truly embody the geodatabase model.

3 Geodatabase The advantages

The geospatial data model, from the initial CAD data model to the coverage data model, has been developed into a geodatabase data model that is now commonly used for decades. Geodatabase provides a common data interface and management framework for GIS applications, providing capabilities to handle rich data types, apply complex rules and relationships, and access large amounts of geographic data.

The advantages of geodatabase are mainly in the expansion of relational database in this model, which embodies the following aspects:

(1) Geodatabase The geometric characteristics of the stored features to facilitate the development of spatial operational functions in GIS applications, such as locating objects adjacent to features or objects of a specific length, and providing a framework for the geographic coordinate system for defining and managing data in Geodatabase.

(2) Geometric networks (geometric network) in Geodatabase can simulate road transport industry or other utility networks and perform network topology operations.

(3) Geodatabase can define an association (relationships) between objects and features. Using topological relationships, spatial representations, and general associations, users can define not only the characteristics of features, but also the association rules for features and other features. When a feature is moved, modified, or deleted, the user's pre-defined contextual features change accordingly.

(4) Geodatabase enhances the integrity of attributes by defining domains (domain) and validation rules (Validation rule).

(5) Geodatabase binds some "natural" behaviors of features to the table where the features are stored.

(6) Geodatabase can have multiple versions (version), allowing different users to edit the same data at the same time, and automatically reconcile conflicts that arise.