Version Control with Git

Object Store Pictures

Let’s look at how Git’s objects fit and work together to form the complete system.

The blob object is at the “bottom” of the data structure; it references nothing and is referenced only by tree objects. In the figures that follow, each blob is represented by a rectangle.

Tree objects point to blobs, and possibly to other trees as well. Any given tree object might be pointed at by many different commit objects. Each tree is represented by a triangle.

A circle represents a commit. A commit points to one particular tree that is introduced into the repository by the commit.

Each tag is represented by a parallelogram. Each tag can point to at most one commit.

The branch is not a fundamental Git object, yet it plays a crucial role in naming commits. Each branch is pictured as a rounded rectangle.

Figure 4-1 captures how all the pieces fit together. This diagram shows the state of a repository after a single, initial commit added two files. Both files are in the top-level directory. Both the master branch and a tag named V1.0 point to the commit with ID 8675309.

Figure 4-1. Git objects

Now, let’s make things a bit more complicated. Let’s leave the original two files as is, adding a new subdirectory with one file in it. The resulting object store looks like Figure 4-2.

Figure 4-2. Git ...