Extended Spreadsheet Database, ESSBASE, is a multidimensional database management system. Essbase was developed by the company, Hyperion, which is now acquired by Oracle. There are several modules of Hyperion, Essbase being of the the primary ones.
There are several key things we need to learn before we go deeper down into learning Essbase.
Some Acronyms:
OLTP: Online transaction processing.
OLAP: Online analytical processing.
ROLAP: Relational OlAP. Business Objects is a very good example.
MOLAP: Multidimensional OLAP. Essbase is what we are talking about here.
DOLAP: Desktop OLAP
HOLAP: Hybrid OLAP
XOLAP: Extended OLAP

The star schema in Essbase is very important without which we cannot think about learning Essbase.
Note: We cannot have more than one fact table in an Essbase star schema.
It has the 'fact table' at the center and other dimensions around the fact table. For example, dimensions such as TIME, REGION, CUSTOMER, PRODUCT, etc.

There are two types of dimensions in ESSBASE: Standard and Attribute.

Standard dimension is the one which defines the core components of business plan: examples are time, customer, product, accounts, regions, etc.

Attribute dimension is the one which defines the characteristics of standard dimension. For example, the colors, type, etc are attritube dimensions. For example, Under the product cars, we can have Honda Civic, Honda Jazz, etc. And we can have attributes such as

Honda Civic (black, 3500 cc) and Honda Jazz (red, 3000 cc) etc. So these are the attributes.

There are 4 types of attributes: Text, numeric, date, and boolean.

Hierarchy and relationship are very important is Essbase.
Look at this tree:
Year
H1
QTR1
jan
feb
mar
QTR2
april
may
june

H2
Here, year is the dimension and the others are the members within the dimension, year.
We see relationships here.
Parent-child relationship: Year is the parent and H1 is its child. QTR1 is the child of H1. jan and feb are siblings.

Generation references: Year is G1, H1 is G2, QTR1 is G3, and so on.

Level references: The last in the tree which does not have any child is level 0. Here Jan is level 0, whereas QTR1 is level 1, etc.

Standard dimension is further divided into two types:
Dense dimension: which has high probability of data occupied.
Sparse dimension: which has low probability of data occupied.

Story of Essbase

The Introduction of Essbase

Essbase - An Overview