SDM is a high-level semantics-based database description and structuring formalism designed to capture more meaning of an application environment than traditional database models. It allows for a more natural and direct incorporation of semantics into database schemas, enabling multiple views of the same information and supporting complex database applications. SDM serves as a formal specification tool, a conceptual model, and a basis for user interfaces and new database management systems. It addresses limitations of existing models by providing a richer set of features for modeling application environments, supporting relativism, abstract entities, and flexible schemata. SDM allows derived information to be embedded in schemas, simplifying database manipulation and enabling new applications. It supports various types of interclass connections, including subclass and grouping connections, which allow for flexible and integrated schema definitions. SDM also includes mechanisms for defining derived attributes and mappings, enabling complex attribute derivations and efficient data retrieval. The paper presents a detailed specification of SDM, its applications, and underlying principles, emphasizing its ability to capture and express the structure of application environments in database schemas.SDM is a high-level semantics-based database description and structuring formalism designed to capture more meaning of an application environment than traditional database models. It allows for a more natural and direct incorporation of semantics into database schemas, enabling multiple views of the same information and supporting complex database applications. SDM serves as a formal specification tool, a conceptual model, and a basis for user interfaces and new database management systems. It addresses limitations of existing models by providing a richer set of features for modeling application environments, supporting relativism, abstract entities, and flexible schemata. SDM allows derived information to be embedded in schemas, simplifying database manipulation and enabling new applications. It supports various types of interclass connections, including subclass and grouping connections, which allow for flexible and integrated schema definitions. SDM also includes mechanisms for defining derived attributes and mappings, enabling complex attribute derivations and efficient data retrieval. The paper presents a detailed specification of SDM, its applications, and underlying principles, emphasizing its ability to capture and express the structure of application environments in database schemas.