# Topology graph XML
Source: [https://docs.qualcomm.com/doc/80-88500-4/topic/128_Topology_graph_XML.html](https://docs.qualcomm.com/doc/80-88500-4/topic/128_Topology_graph_XML.html)
The hardware and software image processing nodes are required to produce desired
output, and the connections between those nodes determine how data flows through the camera
subsystem. This set of nodes and connections is called a topology.
A use case is defined by a set of targets to be processed, and a set of per-session settings
which further define how the data should be processed. Each use case is represented by a
topology, which is the connection between the information passed into the HAL3 API, and the
concrete definition of how to process the data. The list of all the use cases and their
corresponding topologies are encoded in an XML file. A use case is selected during
configure\_streams based on two sections in the XML and an XSD schema, which defines the
structure of the XML, is provided. Tools are provided to package the XML files as an offline
binary for consumption by the CHI driver.
Figure : Relationship between nodes, ports, and links
For additional information, see the following documents:
- For information on generating new use cases in XML, see Qualcomm Spectra ISP Camera
CHI API Reference (80-PC212-1).
- For information on generating custom CHI nodes, see CHI Customization Guide
(80-PN984-4).
**Parent Topic:** [Camera](https://docs.qualcomm.com/doc/80-88500-4/topic/122_Camera.html)
Last Published: Aug 18, 2023
[Previous Topic
CHI architecture model](https://docs.qualcomm.com/bundle/publicresource/80-88500-4/topics/127_CHI_architecture_model.md) [Next Topic
CamX](https://docs.qualcomm.com/bundle/publicresource/80-88500-4/topics/129_CamX.md)