why is spatial database required. while the features in GIS software's have attribute table that can be query, edit, inserted, deleted.
then why is oracle spatial or POSTGIS(sql)used to store spatial features
The two works hand in hand. The two being the Oracle Spatial (RDBMS) and the GIS software's database (geodatabase).
A multiuser geodatabase utilizes a multitier architecture that implements advanced logic and behavior in the application tier (e.g., ArcGIS software) on top of a storage tier (e.g., relational database management system [RDBMS] software). The responsibility for managing geographic data in a multiuser geodatabase is shared between the GIS application tier and the RDBMS software.
A relational database management system (RDBMS) provides a straightforward formal structure for storing and managing information in tables. Data storage and retrieval are implemented with simple tables. The multiuser geodatabase utilizes the power of the RDBMS. Certain characteristics of geographic data management, such as disk-based storage, definition of attribute types, query processing, and multiuser transaction processing, are delegated to the RDBMS.
The multiuser geodatabase uses an RDBMS to provide you with:
+ Flexibility to store your data in a supported RDBMS of your choice
+ Ability to apply your existing IT knowledge and experience to manage the environment through common RDBMS practices
+ Spatial types to enhance data storage and interoperability
I hope this helps.