expressor Schemas describe a reusable structure of attributes (active metadata) that is read from or written to the selected data source/target before or after processing in a Dataflow.
Simply stated, they are used to define how the data structure looks to the up stream and down stream Operators used in an expressor Dataflow. It represents a structured, reusable and consistent approach to eliminating the need to change the underlying Dataflow if something in the source or target was to change.
A Delimited Schema defines the data structure (active metadata) for files whose attributes are separated by a delimiting character such as commas, pipe, tabs, space etc. You create this when using Read and Write File and Custom Operators. You will need a File Connection defined to use these.
A Table Schema defines the data structure (active metadata) of the table to be used in the dataflow. You create this when using Read, SQL Query, Write Table Operators and Custom Operators. You will need a Database connection defined to create these.
Schemas can be shared and saved as types to be reused with other operators and dataflows. By Default all NEW schemas are created as Local Composite Types with the name Local1. This is the default representation of the logical data or semantic model that is used in the dataflow flow.
When opening a schema to view or modify its attributes or mappings you will see a right and left view. The left view is how the data looks from the defined source (external physical strcuture), the right is the Semantic Type or logical view of how the attributes will be represented in the Dataflow. This is NOT your typical SOURCE to TARGET mapping. This is the definition of the attributes in the Dataflow and how they will be represented to the next operator. Additionally, mappings containing inline constraints, transformation, error handling and validation can be created by either selecting a mapping arrow and clicking Edit Mapping or by selecting an attribute in the Semantic type and clicking Edit in the Attributes section in the button ribbon above.