Which component is necessary for integrating external data sources in Appian?

Integrating external data sources in Appian is primarily facilitated through data stores. Data stores act as a connection point for Appian to access, store, and manipulate data from external databases or sources. They allow for the creation of entities that represent the structure of external data and allow you to perform operations such as reading, writing, and updating data seamlessly within your Appian applications.

Choosing data stores as the necessary component highlights their essential role in data integration, as they provide the underlying framework to connect and interact with data sources. This integration is critical for ensuring that applications can utilize real-time data from various systems, thereby improving functionality and user experience.

The other options, while important in their contexts, do not specifically serve the purpose of integrating external data sources. Expression rules are used for encapsulating logic and computations, process models handle workflow and business processes, and task nodes relate to user interactions within those workflows. Therefore, they do not directly contribute to the integration process as data stores do.