The Core Data Services comprise a family of domain-specific languages (highlighted in the illustration above) which serve as a common core model for all stacks on top:The Data Definition Language (DDL) for defining semantically rich domain data models which can be further enriched through Annotations. The Query Language (QL) for conveniently and efficiently reading data based on data modelsas well as for defining views within data models. The Expression Language (EL) for specifying calculated fields, default values, constraints, etc.within queries as well as for elements in data models Besides these DSLs, Core Data Services also comprise advanced means for writing data, handling transactions, access control – yet these services are not yet specified in details as of now. Core Data Services focus on providing functional services independent of any programming language and language paradigms. They don't specify nor make assumptions on how to add application logic and behavior using general-purpose programming languages and services of application containers.Further background – not necessarily for presentation:The CDS data definition language supports for example: Definition of reusable structured typesStructured fields (instead of flat tables)Calculated fieldsAssociations between entities, that can be used to explicitly model the structural relationships between data. This information can be used when writing queries in the CDS query language. Since path expressions can be used instead of SQL joins, queries are much easier to write and understand. A modification-free extension mechanism that can be used by add-on developers, partners or customers to add fields to entities and views, for example.Annotations for defining different types of metadata. CDS Core annotations are available for example for metadata describing hierarchies, for translatable field labels to be shown in user interfaces, for hints for compilers and generators, and in the future also metadata for analytical clients (attributes, measures, hierarchies, default aggregation). In addition, domain-specific annotations will be available. Domain-specific annotations can, for example, be used to annotate a field of a business entity with information about the kind of data it contains, for example whether it is a URL, a name, an amount, or a quantity. Such metadata can be used by user interfaces to adjust the display and interaction accordingly. CDSviews based on existing tables (created by previous releases or via replication) to make the data available in the CDS world and to model additional semantics such as associations. Reflection. It is planned to give applications access to metadata using the CDS query language.
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