Work with data using code in Common Data Service for Apps
Common Data Service (CDS) for Apps has entities that are used to model and manage business data. You can use standard entities or create your own custom entities to store data.
Use web services to work with data
CDS for Apps provides two web services that you can use to interact with data: Web API and Organization Service. Choose the one that best matches the requirement and your skills.
The Web API is an OData v4 RESTful endpoint. Use this for any programming language that supports HTTP requests and authentication using OAuth 2.0.
More information: Use the Common Data Service for Apps Web API
Use the .NET Framework SDK assemblies for projects that involve writing plug-ins or workflow extensions.
More information: Use the Common Data Service for Apps Organization Service
Use the Xrm.Tooling assemblies if you are creating a Windows client application. More information: Build Windows client applications using the XRM tools