# Overview

This article describes the following:

**What are the basic building blocks of a Logica model?**

Logica models are built with just two basic elements: **nodes** and **links.**

**What are nodes?**

**Nodes store values**, which can be numbers, text, boolean or dates.

**Nodes have a time dimension**, which can be months, years or custom.

**Variables are nodes that have values that change over time**. Each time period can store a unique value.

**Constants are nodes that have values that do not change over time.** Each time period has the same value.

**What are links?**

**Links transfer values**

*between two nodes.*

**Links can shift values over time**.

**Links can transform values. **

**How are nodes and links combined?**

**Nodes and links are combined to create a graph, or logical tree.**

**The graph is essentially one big formula. **When any input value is changed, The calculation is automatically triggered, and updates the values of affected nodes after iterating through all time steps.

**What's Next?**

Learn more about building calculations with Nodes and Links.