To show you what the tangle looks like when everyone uses this random selection strategy (technically called “uniform random tip selection”), we’ve made a visual simulation of it. Each incoming transaction looks at all the currently unapproved transactions, and simply chooses two at random. However, to make our lives easier, we’ll start with the simplest strategy: choosing randomly between all available tips. The strategy for choosing which two tips to approve is very important, and is the key to IOTA’s unique technology. Each incoming transaction needs to choose two tips to approve (there is always at least one!). In the example, transaction number 6 is a tip, because no one approved it yet.
![iota tangle iota tangle](https://miro.medium.com/max/2000/0*qnfNTfgm2qqr-wBb.jpg)
At this stage we won’t worry too much about what we mean by approving a transaction, as we’ll get into that later. Transactions are more or less what you would expect, information of the form “person A gave person B ten IOTAs”. In the example above, transaction number 5 approves transactions number 2 and 3. When a new transaction joins the tangle, it chooses two previous transactions to approve, adding two new edges to the graph. Each transaction is represented as a vertex in the graph. The Tangle, which is the data structure behind IOTA, is a particular kind of directed graph, which holds transactions.
![iota tangle iota tangle](https://m.media-amazon.com/images/M/MV5BNzQ3MTk3ODEwMV5BMl5BanBnXkFtZTcwNzAwOTM0OQ@@._V1_UY1200_CR766,0,630,1200_AL_.jpg)
A directed graph is a collection of vertices (squares), which are connected to each other by edges (arrows). To understand the tangle, we need to learn about what computer scientists call a directed graph. In this article, we introduce the Tangle, explain what it is, and how we study it mathematically in the IOTA research team. We will loosely follow the whitepaper, but go a bit slower and add some pictures to clarify the basic concepts.
#Iota tangle series
This is the first in a series of beginner level posts, aimed at those who want to learn more about how IOTA works under the hood.