DEV Community: Joseph Okwemba

Schemas and Data Modeling in Power Bi

Joseph Okwemba — Sun, 01 Feb 2026 16:49:07 +0000

The blue print for High-perfomance Analytics
Effective data modelling is foundation of reliable analytics. Regardless of how advanced your visualisation are, a poor model leads to slow reports and inaccurate insightst. This article explore the esseential architecture of Power BI: Schemas, Tables, and Relationships.

The core Building Blocks

Power BI uses the Vertipaq in memory engine, Which thrive on structred data. To leverage this, you must categorize your table into two roles:

Fact Tables: These store quantitative events (e.g., sales, Temparature rreading, or Tickets). They are long "long," containing millions of rows with numeric values to be aggregated.
DImension Table: These provide context (e.g.,Date, Product, or Geography). They are "wide," containing descriptive attribute used for slicing and dicing.

Choosing The Roght Schema

The Star Scheme (Best Practise)

In the star schema, A central FAct table is surrounded by Dimension tables.

-Why it works: it's the most effecient for POwer BI. It minimize the number of "joins" the engine must perform, resulting in lighting-fast calculations.

-The verdict: Always aim for this.

The Snowflake Schema

A snowflake shema occurs when dimensions tables are normlized(e.g., a product table links to a category table).

The Downside:While it saves space, It forces Power BI to perform multiple joins, which can drag down performance and make DAX measure much harder to write.

The Power BI Audit Checklist

Feature	Best Practice	Red Flag (Avoid)
Relationship	One-to-Many (1 : *)	Many-to-Many (* : *)
Filter Direction	Single (Dim → Fact)	Bi-directional (Both)
Schema Type	Star Schema	Flat / Wide Tables
Granularity	Consistent across tables	Mixed levels of detail

Common Pitfalls and How to Fix Them

Problem "My totals are wrong when i use a specific slicer."

The Fix:Check your Relationship Direction. Ensure your dimension id filtering the fact table, not the other way round.

Problem: :Power BI says there is a 'circular Dependancy'"

The Fix: Thisusually happens with Bi-directional filters. Change your cross-filter to "single" to restore a logical data flow.

Why This Matters for Your Business

Perfomance: Well-modeled load in milliseconds, even with millions of row.
Accuracy A star schema prevent "double-counting" and ensure DAX logic remains simpleand predictable.

3.Self-Service: when the model is clean, non-technical users can build their own charts without breaking the data.

Visual Aid Recommendation

Introduction to Micrososft Excel for Data Analytics

Joseph Okwemba — Sat, 24 Jan 2026 17:31:59 +0000

Microsoft excel is one of the easiest tool to use when starting with data analytics. It helps to organise data, perfom simple analysis, and present result clearly. In this article, I explain how excel can be used for basic data analysis using simple examples.

Opening and viewing data on excel

📸 Screenshot 1: Excel workbook with dataset opened
The first step is data analysis using excel is opening dataset. Once the file is opened, the data appears in the raw and columns. Each column represesnts a type of information, such as names, location, or values.
Having data well arranged make it easier to work and analyze.

Understanding Raw, Columns, and Cells

📸 Screenshot 2: Excel sheet showing column headers and rows
Each box in excel is called a cell. Row run horizontally, while column run vertically. column headers help identify what type of data is stored in each colum.
This structure allow data to be organized clearly.
Example of rows, columns, and a selected cell in Excel

Sorting Data

📸 Screenshot 3: Sort option selected from the Data tab
Sorting is used to arrange data in a specific order. For example, Data can be sorted alphabetically or Numeric.
Sorting helps quickly identify highest, Lowest, or grouped values.
Data sorted in Excel to organize information more clearly.

Filtering Data

📸 Screenshot 4: Filter applied to a column
Filtering allows users to display only specific information. For example filtering can be used to show data from one location only.

this help focus on relevant data without deleting anything.
Filtering data in Excel to display only specific records.

Using Basic Formulas

📸 Screenshot 5: Formula bar showing SUM or COUNTIF
Excel formulas help perform calculations automatically. Common formulas include:
SUM for adding values.
COUNT or COUNTIF if for counting entries
AVERAGE for calculating the mean.
Formulas makes analysis faster and reduce manual errors.
Click an empty cell

Enter a formula such as:

=COUNTIF(P:P,"Nairobi")

=COUNTIFS(P:P,"Nairobi",O:O,"Intern")

Using an Excel formula to analyze data

Creating Charts

📸 Screenshot 6: Bar or column chart created from data
Chart helps turn data into visual information. Excel allow users to create charts such as bar chart and pie charts.
charts makes it eaiser to compare values and understand trends.
Chart created in Excel to visually represent the data.

Formatting Data

📸 Screenshot 7: Formatted table with bold headers and colors
Formatting helps improve readability. This include bolding headers, adjusting column width, and applying number formatts.
Well-Formatted data is easier to understand and looks more professional.

Formatted dataset to improve readability and presentation.

Conclusion

📸 Optional Screenshot: Final dataset or chart
Microsoft excel is a useful tool for basic data analytics. It help organize data, Perfomr simple analysis, and present result clearl. For beginners, Excel is good strating point before learning advance data analyiss.

Understanding Git and GitHub: A Beginners Guide

Joseph Okwemba — Sun, 18 Jan 2026 06:06:06 +0000

What is Git?

Git is version control system that helps you keep track of changes in made to your code. Instead of saving many copies of the same project, Git record each changes and store it as part of the project history.
with git you can always go back to an earlier version of your code if something goes wrong. Git works locally on your computer and does not need internet to track changes.

Why version control is important

version control is important for several reasons

it helps you avoid loosing your work
You can see what changes were made and when
It allows Multiple people to work on the same project
You can easily fix mistakes by going back to previous version In real software project, Version is necessary because code change is always changing.

Git and GitHub Difference

Git and GitHub are not the same thing

Git is the tool that track and changes your computer
GitHub is an online platform where you store and share your Git project you use Git commands to send your code to GitHub or get code from GitHub

Seting up Git on your computer

Before using Git, you need to make sure it is installed and configured.

Check Git version

To confirm Git is installed:

git --version

Configure your Name and Email

Git uses this information to track who made changes.

git config --global user.name "joseph" 
git config --global user.email "joseph@gmail.com"

To confirm the configuration :

git config --global --list

Setting up HHS

SSH allow you to connect to GitHub securely without entering your password every time.

Generate HHS key

ssh--keygen -t ed25519 -C joseph@gmail.com"

Press enter to accept the default file location.

Start the HHS agent

eval "$(ssh-agent -s)"

Add SSH key

ssh-add ~/.ssh/id_ed25519

Copy the public key

cat ~/.ssh/id_ed25519.pub

Copy the output and add it to GitHub → setting → SHH → and GPG key.

How to push GitHub code

First, open your project in the terminal

Step one

Step 1: Initialise Git

git init

Step 2: Check file status

git status

Step 3: Add File

git add.

step 4: Commit changes

git commit -m "My first commit"

Step 5 : Connect to GitHub Repository

git remote add origin https://github.com/username/repository-name.git

Step 6: Push the code

git push -u origin main

your code will now appear on GitHub

How to pull code from GitHub

pulling means getting the latest version of the project from giHub

git pull origin main

this is usefully when working others or when switching devices

How to track changes using Git

To see changed files

git status

To see what exactly changed.

git diff

To view commit history

git log

This commands help you understand how your project has changed over time

conclusion

Git is very important tool for developers. It helps you manage your code, track changes, and work with others.

Luxdev Markdown Language Class

Joseph Okwemba — Tue, 13 Jan 2026 11:00:02 +0000

How to right a markdown language

this is the first markdown language the students have learned and they can now write an article on dev.to

The first things students learned

the student have learned how to write a heading

lastly but not leat

she/he tolld me that they love tech and i responded i enjoy tech too.
-Morning class
-Evening class

*name = "kaleb"

Here is where you wiil find me; visit my linkedIn account on