  Emergency-relevant data comes in many varieties. It can be high volume and
high velocity, and reaction times are critical, calling for efficient and
powerful techniques for data analysis and management. Knowledge graphs
represent data in a rich, flexible, and uniform way that is well matched with
the needs of emergency management. They build on existing standards, resources,
techniques, and tools for semantic data and computing. This chapter explains
the most important semantic technologies and how they support knowledge graphs.
We proceed to discuss their benefits and challenges and give examples of
relevant semantic data sources and vocabularies. Natural-language texts -- in
particular those collected from social media such as Twitter -- is a type of
data source that poses particular analysis challenges. We therefore include an
overview of techniques for processing natural-language texts.
