Data Warehousing: Tutorial 6 [Staging Area, ETL, DSO and Data Mart]


Welcome back to our data warehousing series! In today’s tutorial, we’ll be diving into some key components of data warehousing, namely the staging area, ETL (Extract, Transform, Load) processes, DSO (Data Store Objects), and data marts. Each of these elements plays a critical role in managing and organizing data effectively for insightful analysis. Whether you’re a seasoned data professional or just starting your journey in the data sphere, this discussion will offer valuable insights and deepen your understanding of data warehousing. So, grab a cup of coffee, and let’s get started!

In the previous tutorial on data warehousing, we learned about star schema and snowflaking.

Alright, let’s give you a quick rundown of what we’ll be discussing today. First up, we have the “Staging Area” – this is like a prep kitchen for data, where it’s cleaned and organized before being served up for analysis. Next, we’ll delve into “ETL”, which stands for Extract, Transform, Load. Think of ETL as the conveyor belt in a production line, moving data from its raw form, reshaping it, and finally loading it into our data warehouse. Then, we’ll touch on “DSO” or Data Store Objects. These are the containers in our warehouse where we keep our transformed data safe and easily accessible. Lastly, we’ll explore “Data Marts”, specialized sections of the warehouse where data is stored in a way that’s specific to the needs of different teams or departments in a business. Each of these components is a crucial cog in the data warehousing machine, so let’s dive in and unpack them one by one.

In this tutorial, we will discuss the basic components of data warehouse. The components constituting the data warehouse structure were mentioned briefly in Data Warehouse tutorial-1. These components have a flow of data:

Source system-> Staging Area-> ODS-> ETL Process-> Presentation Area

data flow

1. Staging Area

The Staging Area is an essential initial component in the data warehousing process. In essence, it’s a temporary space where data from multiple sources is gathered before it undergoes the transformation process. The data here is raw, unprocessed, and often in different formats, representing a myriad of sources from where it originates. The primary purpose of a staging area is to ensure a smooth and efficient ETL process. It does this by cleaning and organizing the data, removing redundancies, and ensuring data consistency. To put it simply, the staging area is like the backstage of a theater, where all the props are gathered and arranged before they make it to the main stage. Similarly, the staging area prepares the data, ensuring it’s in the right format and condition before it’s loaded into the data warehouse for analysis and reporting.

How Staging Area Works in a Data Warehouse

In the context of a data warehouse, the Staging Area works as the intermediary zone that mediates the inflow of data from various sources. When data is initially pulled into the data warehouse, it lands in the staging area. This is where data gets cleaned, transformed, and made ready for loading into the Data Store Objects. Essentially, the staging area acts as a buffer between raw data and the main warehouse, preventing the direct dumping of possibly unorganized and unclean data into the data warehouse.

The staging area’s role does not end here. It also provides a safety net in case of data load failure. What this means is that if an ETL process fails for any reason, the data in the staging area remains intact, and the ETL process can be restarted again from this point. Without a staging area, we would need to extract the data all over again from the source systems, which could be time-consuming and resource-intensive. Therefore, the staging area not only enhances the efficiency of the ETL process but also contributes towards making the entire data warehousing process more reliable and robust.

Importance of Staging Area in the Data Warehousing Process

The Staging Area plays a crucial role in the data warehousing process, acting as the initial buffer that absorbs the raw, unprocessed data from diverse sources. This intermediary zone offers many advantages that make it an integral part of the data warehousing architecture.

Firstly, it ensures data quality by enabling data cleaning and transformation before loading into the Data Store Objects (DSO). This process helps to standardize the data formats, making it more consistent and reliable for analysis.

Secondly, it enhances the efficiency of the data warehousing process. By performing preliminary operations on data within the staging area, we reduce the computational load on the main warehouse, allowing it to focus on critical tasks such as data analysis and reporting.

Lastly, the staging area also offers a layer of protection against data load failures. If an ETL process fails, the data stored in the staging area remains unaffected and can be reprocessed, eliminating the need to re-extract data from the source systems. This feature makes the entire data warehousing process significantly more robust and reliable.

The staging area is pivotal to a data warehouse’s functioning, offering data quality assurance, operational efficiency, and robustness against process failures.

2. ODS

ODS stands for Operational Data Store. It is a place where the integrated copies of operational data are stored. ODSs are updated on a frequent basis. It can be used to prepare operational reports and to feed the operational data to the data warehouse. It is used for real-time processing. Data from data warehouse can also be used in ODS.

An Operational Data Store (ODS) is another critical component of data warehousing. Unlike the traditional data warehouse where data is integrated for reporting, the ODS contains granular, operational, and transactional data in a relatively current state. In essence, it is a volatile, subject-oriented, and integrated dataset designed for real-time, operational reporting needs.

The role of ODS in data warehousing is multifold. First, it acts as a bridge between original data sources and the data warehouse. It provides an intermediate staging area where data from various sources is consolidated, cleaned, and integrated before being stored in the data warehouse. This ensures the reliability of data and enhances its accessibility for the ETL process.

Moreover, ODS supports tactical decision-making in an organization. By providing a near-real-time view of the business operations, ODS allows managers to make more timely, informed decisions. This can be particularly useful in situations where the decision-making window is narrow, and access to up-to-date, operational data is critical.

Finally, ODS contributes to data consistency across an organization. By integrating data from multiple sources into a single, unified view, it reduces data redundancy and conflicts, hence improving data quality and integrity. So, in a nutshell, the ODS forms an essential part of the data warehousing process, facilitating real-time reporting and decision-making, and enhancing data quality and consistency.

ODS thus can be considered an interface between operational system and data warehouse or can be used as a partition of data warehouse itself. It can also be defined as a place where granular atomic data can be stored.


3. ETL (Extract, Transform, Load)

Diagram depicting the flow of conventional ETL. This was recreated from the Data Warehouse ETL Toolkit by Ralph Kimball and Joe Caserta. Remyrosenbaum – Own work CC BY-SA 4.0 DEED

The ETL (Extract, Transform, Load) process is the backbone of any data warehousing operation, acting as the conduit that moves data from its original sources to the data warehouse. It’s a three-step journey, each step playing a vital role in preparing data for analysis and business intelligence.


The ‘Extract’ stage involves pulling data from various source systems, which could range from databases and CRM systems to cloud-based applications. This raw data could be structured, semi-structured, or unstructured, depending on the source.

It is a process that involves reading and understanding the source data. It also involves copying the source data which can be put into the staging area for further manipulation.


‘Transform’ is the stage where the real magic happens. It’s here that the data is cleaned, validated, and converted into a consistent format. This stage may involve removing duplicates, validating and correcting values, and creating derived values. Essentially, it’s all about refining and preparing data to ensure it’s reliable and useful for analysis.

During the ETL process, a number of processes occur under transformation:

  1. Cleansing data – Correcting spelling, checking missing data, checking & resolving the domain conflicts.
  2. Combination of data from multiple sources.
  3. Deduplication of data.
  4. Assignment of warehouse keys.


Finally, the ‘Load’ stage is where the transformed data is loaded into the target destination—usually a data warehouse or a data mart. This stage needs to be managed carefully to ensure the smooth and successful transition of data, and to avoid overloading the systems.

The integrated data is loaded into the presentation area of data warehouse. Before loading the transformed data, if the data is normalized, it is termed as enterprise data warehouse.

Data staging area also involves sorting and sequential processing of data. It may consist of flat files. It consumes lots of time and is more costly. It is better to improve the presentation area than taking time in normalizing the data before loading to the presentation area.

Loading is basically the process of loading the data in the data warehouse to each of the data marts. Indexing should be there in the data mart before arrival of data for better query performance. Thus the loaded data is indexed and supplied for publishing.

To summarise, the ETL process is a key part of data warehousing, responsible for the extraction of data from various sources, transforming it into a consistent, usable format, and loading it into a data repository. It ensures that your data is not only accessible but also reliable and meaningful for further analysis and decision-making.

Role of ETL in Data Integration and Management

ETL’s role in Data Integration and Management is paramount in the world of data warehousing. Data integration involves combining data from different sources and delivering them in a unified view. Here, the ETL process shines by extracting data from disparate sources and transforming it into a uniform format, thus facilitating data consistency. This uniformity simplifies the process of integrating data from various departments, making it easier for businesses to analyze and draw insights from their data.

In terms of Data Management, ETL helps maintain data quality, which is crucial for reliable analysis and decision making. The transformation stage, where data cleaning and validation occur, helps rid the data set of inaccuracies, inconsistencies, and duplications, thereby enhancing its quality and reliability. Also, ETL provides a systematic way to load data into a data warehouse or data mart, making data easy to manage, access, and utilize. Therefore, through the ETL process, businesses can ensure they are drawing from accurate, high-quality data for their strategic decision-making processes.

4. Data Mart and Presentation Area

The Data Mart is a specialized subset of a data warehouse that focuses on a specific business line or department. It’s like a mini data warehouse designed to perform specific queries and generate relevant reports for specific business users. The primary purpose of the Data Mart is to help business users make informed decisions that improve their operational efficiency. It simplifies access to data, reducing the time and computational resources needed to extract useful insights.

The Presentation Area, on the other hand, is the final stage in the data warehousing process. It’s where processed and organized data is made available for end-users in a readable and accessible format. The data contained in this area is ready for querying and analysis. It is typically presented in the form of dashboards, reports, or charts, which help users visualize and interpret data effectively. In essence, the Presentation Area is the space where business intelligence becomes actionable, as users can access, interact with, and draw insights from the data to inform their decision-making processes.

The Data Mart and the Presentation Area play key roles in turning raw operational data into actionable insights, ultimately driving more effective business decisions.


Data Warehousing, with its integral components – Staging Area, ETL, DSO, and Data Mart, is a transformative tool that empowers businesses to leverage their data for strategic decision-making. By ensuring that data is stored, organized, and processed effectively, data warehousing enables the creation of high-quality, actionable insights. Whether streamlining operations, identifying new market opportunities, or driving customer engagement, these insights serve as the backbone of data-driven decision-making. Adapting to a data-driven approach not only fuels business growth but also fosters a culture of innovation and agility. As we continue to generate and interact with data at unprecedented rates, the importance and value of effective data warehousing will only escalate, becoming a cornerstone of successful business strategy.

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