There are three types of geo-databases, which in itself refers to a kind of container for storing datasets. The first one is File geo-database, which refers to the filing system containing folders. Each file can hold up to 1 TB, which is recommended in place of personal databases.
The second type is called a Personal geo-database, which refers to stored datasets within the Microsoft Access file system, with the maximum file size limited to 2GB. The third one is known as ArcSDE geo-database, which seeks storage using such systems like Oracle, IBM DB 2, Microsoft SQL Server, Postage SQL, or IBM Informix. Being multi-user, such geo-databases make use of ArcSDE which takes away any limitation in size or number of users.
Let us now consider some of the important features of the ArcSDE database in GIS applications. This is a group of GIS datasets, in the form of tables in a relational database. It allows many users to write and read, and as pointed out its format for storage can be varied. Its size can go as per DBMS limits, it wholly supports all DBMSes, allowing for replication of cross-database, historical archiving and allows updating by checking in and checking out methods.
The operating system platforms used by ArcSDE databases are varied; Windows, Linux, many variants of UNIX can all host the DBMS. Permissions and security to access the database are set and stored on the DBMS.
ArcSDE database technology is required for administration for this kind of geo-database, as it can help full functions of backup, recovery and replication, etc.. ArcSDE for SQL Server Express comes with ArcGIS Engine, ArcGIS Server, ArcEditor and ArcInfo for all workgroups.
Thus ArcSDE database for GIS is considered as one of the best geo-database solutions for GIS applications.