Chapter 2. SCR Tree

Chapter 2. SCR Tree
	Access to the System (SCR in General)

As a computer's hardware and software configuration is quite complex, the SCR organizes all data in form of a tree. It resembles very much a file system with its folders, sub-folders and files whereby the tree structure reflects the thematic separation of the various configuration categories.

The SCR-tree consists of two different kinds of nodes:

Table 2.1. SCR Node Types

Data nodes	Data nodes represent single pieces of data, for example a `sysconfig`-entry or a mountpoint of a file system in `/etc/fstab`. They are the leaves of the tree and stand for actual data to be handled.
Map nodes	Map nodes allow for navigation to the leaves just like the path components in the directory structure of a file system. This way map nodes are used to structure the data in a suitable manner.

The names of the nodes in the SCR-tree can be concatenated resulting in the creation of an SCR-path. An SCR-path is a description were to find a node in the SCR-tree. It is a sequence of path components each of them being a string. As we have seen in the section Data type path YCP-paths are prepended by dots (.) which act as separators in compound paths. So .foo.bar is a valid YCP-path. If bar is an SCR data node, then SCR::Read(.foo.bar) would render some data. If bar is a map node, then SCR::Dir(.foo.bar) would reveal the immediate sub-nodes in the SCR-tree, e.g. ["big", "brown", "fox"]. The single dot (.) is also valid and denotes the root of the whole SCR-tree. Consequently SCR::Dir(.) will return a list of all the top-nodes in the SCR-tree.

In the figure below we see a (very small) cut-out of the SCR-tree that is related to hardware-specific information.

Figure 2.1. SCR Hierarchy Tree

The light gray nodes are SCR-map-nodes denoting the path to the data. They can be used with SCR::Dir(...) to find out what is below. So in the figure above SCR::Dir(.probe) would return a list as [..."has_smp", "boot_arch", "has_apm"...].

The dark grey nodes are SCR-data-nodes that stand for the actual data. What can be done with them depends on the actual node (reading, writing, executing), but usually SCR::Read(...) is possible. As is shown above SCR::Read(.probe.boot_arch) would return "grub".