## JSDAI Introduction

# Overview of the SDAI management object

In the previous examples we already learned about

- SdaiSession, the root from which every SDAI activity starts from
- Implementation, to provide version and level information of the implementation
- SdaiTransaction, to control simultaneous updating of changes
- SdaiRepository, the physical storage container for SchemaInstances and SdaiModels
- SdaiModel, to group entity instances based on one express schema

Further management classes are

- SchemaInstance as a logical grouping of models to define a valid population of an express schema
- EntityEntent, an auxiliary class to group entity instances of one entity data type
- SdaiException, thrown in case of error conditions

The most important entities of the dictionary schema, needed for late binding access, are:

- schema_definition
- entity_definition
- attribute

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