What is RDBMS and what is its use in GIS?

Relational Database Management System, RDBMS A database management system with the ability to access data organized in tabular files that can be related to each other by a common field (item). An RDBMS has the capability to recombine the data items from different files, for multiuser access

 A relational database management system (RDBMS or just RDB) is a common type of database whose data is stored in tables.

You’ll find that most databases used in businesses these days are relational databases, as opposed to a flat file or hierarchical database.

Relational databases have the clout to handle multitudes of data and complex queries, whereas a flat file takes up more space and memory, and is less efficient.

So modern databases use multiple tables as standard. The data is stored in lots and lots of tables, or ‘relations’. These tables are divided into rows (records) and columns (fields).

RDBMS is a type of database in which data is organized across one or more tables. Tables are associated with each other through common fields called keys. More information can be extracted using different attributes of different tables. 

A type of database in which data is organized across one or more tables. Tables are associated with each other through common fields called keys. In contrast to other database structures, an RDBMS requires few assumptions about how data is related or how it will be extracted from the database. The relational model has relationship between tables using primary keys, foreign keys and indexes. Thus the fetching and storing of data become faster than the old Navigational model. So RDBMS is widely used by the enterprises and developers for storing complex and large amount of data.

RDBMS: An acronym for DataBase Management Systems. A relational database is a collection of data items organized as a set of formally-described tables from which data can be accessed or reassembled in many different ways without having to reorganize the database tables.What is its use in GIS?

The geodatabase storage model is based on DBMS principles, leveraging a series of simple yet essential relational database concepts. The DBMS (and the file system for file geodatabases) provides a simple, formal data model for storing and working with information in tables.

Key concepts include the following:

• Data is organized into tables.
• Tables contain rows.
• All rows in a table have the same columns.
• Each column has a type, such as integer, decimal number, character, date, and so on.
• Relationships are used to associate rows from one table with rows in another table. This is based on a common column in each table.
• Relational integrity rules exist for tables. For example, each row always shares the same columns, a domain lists the valid values or value ranges for a column, and so on.

For ArcSDE geodatabases that are stored in relational databases, a number of additional DBMS capabilities also apply:

• Structured query language (SQL), a series of relational functions and operators, is available to operate on the tables and their data elements.
• The SQL operators are designed to work with the generic relational data types, such as integers, decimal numbers, dates, and characters.

Each of these includes geodatabase objects that define a generic geographic information system (GIS) model that is shared by all ArcGIS applications and users. The purpose of the geodatabase objects is to expose a high-level GIS information model to clients and to persist the detailed implementation of this model in any appropriate storage model—for example, in standard database management system (DBMS) tables, in file geodatabases, and as extensible markup language (XML) streams.

Geodatabase storage includes both the schema and the rule base for each geographic dataset plus simple, tabular storage of the spatial and attribute data.

The geodatabase schema includes the definitions, integrity rules, and behavior for each geographic dataset. These include properties for feature classes, topologies, networks, raster catalogs, relationships, domains, and so forth. The schema is persisted in a collection of geodatabase meta tables in the DBMS that defines the integrity and behavior of the geographic information.

The spatial representations are most commonly stored as either vector features or raster datasets along with traditional tabular attributes. For example, a DBMS table can be used to store a feature class where each row in the table represents a feature. A shape column in each row is used to hold the geometry or shape of the feature. The shape column holding the geometry is typically one of two column types:

• A binary large object (BLOB) column type
• A spatial column type, if the DBMS supports it

A homogeneous collection of common features, each having the same spatial representation, such as a point, line, or polygon, and a common set of attribute columns, is referred to as a feature class and is managed in a single table.

Raster and imagery data types can be managed and stored in relational tables as well. Raster data is typically much larger in size and requires a side table for storage. For DBMS storage and access, each raster is cut into smaller pieces, or blocks, and stored in individual rows in the separate block table.

The column types that hold the vector and raster geometry can vary from database to database. Recently, most DBMSs have added support for spatial type extensions, and the geodatabase can readily use them to hold the spatial geometry. Esri was closely involved in efforts to extend Structured Query Language (SQL) for spatial types as the primary author of the SQL/MM Part 3 Spatial and the Open Geospatial Consortium, Inc. (OGC) Simple Features SQL specifications. Esri has focused on support for these types, as well as the independent Oracle Spatial, PostGIS (in PostgreSQL), and Microsoft SQL Server spatial types, in the persistence of geodatabases using DBMS standards.