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In a Linux environment where flexibility and customization are required, open source LDAP
solutions such as OpenLDAP are frequently used. There are, however, some drawbacks to using
open source solutions in a Linux environment, including the need for specifically skilled staff;
slowed authentication when large LDAP repositories are in use; and potential system
incompatibility with some devices, applications, and web applications.

Data Storage
Three primary forms of data storage are commonly used, databases, data warehouses, and data
lakes. Databases are the most common and will be discussed in detail below. The difference
between the three types of storage can be described by the source and type of data:

 Database – single source repository; can be structured or unstructured data.
 Data warehouse – multiple sources of data stored in a single repository. Typically, structured
data that is easily retrievable for a defined purpose.

 Data lake – multiple sources of data stored in a single repository. Data is unstructured and
not easily retrievable.

Databases
A database is an organization of data in a manner that allows for easy retrieval and updates.
There are two main types of databases: relational and nonrelational databases.
Relational databases have these characteristics:

 Multiple datasets arranged in a table-based schema of rows and columns.

 Clearly defined relationships among the tables.
 Useful for managing large stores of transactional and related data.
 Data security models allow users to see only what they are authorized to see.

 Can be queried (analyzed) using a simple Structured Query Language (SQL) and in tabular
format, usually using proprietary database software.
Nonrelational or Not Only SQL (NoSQL) databases feature these characteristics:

 Datasets arranged in clusters and nontabular format.

 Accommodates unstructured data in a modern big data environment.
 Simple design for different types of data (e.g., time series, contacts, media).

Relational database management systems (RDBMS) are platforms that allow users to update,
create, append, and delete table data within a relational database. RDBMS platforms are typically
proprietary, requiring licensed use of the platform. Typical RDBMS platforms include Microsoft
SQL Server, IBM DB2, Oracle Database, MySQL, and Microsoft Access.

SQL is a database language used by the RDBMS platforms to interact with (query) data in tables.
An example is shown in Figure 3.

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