> For the complete documentation index, see [llms.txt](https://docs.snomed.org/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.snomed.org/snomed-ct-specifications/snomed-ct-template-syntax-specification/4-logical-model.md).
# Logical Model
A SNOMED CT template is a SNOMED CT expression, expression constraint, or query that contains one or more *slots.* Each template slot either provides information as to how the template should be processed (i.e. an information slot), or serves as a placeholder for a specific value that may be completed at a subsequent time. Each replacement slot may have a replacement type (e.g. concept, expression, token, string, integer, decimal or boolean), a slot name, and a replacement constraint. Depending on the replacement type, the replacement constraint may either be an expression constraint, a value list constraint or a range constraint. Each information slot may have a cardinality and a slot name.
## Logical Model
The SNOMED CT template syntax defines the syntax used for these slots, irrespective of the computable language in which they are embedded. Figure 4-1 below illustrates the abstract model of the SNOMED CT template syntax. Please note that no specific semantics should be attributed to each arrow in this diagram.
Figure 4-1: Abstract model of SNOMED CT Template Syntax
## UML Class Diagram
The figure below provides a non-normative representation of the logical model of the SNOMED CT Template Syntax using a UML class diagram.
Please note that each of the classes in this diagram corresponds to a rule in the syntax specification defined in [Syntax Specification](/snomed-ct-specifications/snomed-ct-template-syntax-specification/5-syntax-specification.md). For a short description of each of these, please refer to [Informative Comments](/snomed-ct-specifications/snomed-ct-template-syntax-specification/5-syntax-specification/5.2-informative-comments.md).
Figure 4.1-1: UML class diagram of template syntax
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