(direct or indirect) specifies on what part of body the procedure is performed. A separate set of rules exist for evaluation procedures. Evaluation procedures are procedures where evidence is evaluated to support the determination of a value, inference or conclusion. Evaluation procedures have additional attributes, such as 'Has specimen','Property' or 'Measurement method'. Event As of 2016, the Event hierarchy does not have a concept model defined. In 2006, some concepts from the 'Clinical Finding' hierarchy were moved to the Event hierarchy. Those concepts retained some of their attributes. (e.g., causative agent) Observable entities SNOMED International is working on creating a concept model for observable entities. Body Structure Body parts represent one of the largest hierarchies within SNOMED CT. The modeling is based on Foundational Model of Anatomy but it differs from the model in some aspects (e.g., region is taken as 3D region and not a 2D region). Important attributes include: 'Laterality', several types of 'Part of' relationships, and 'Is a'. Pharmaceutical / biologic product Pharmaceutical and biologic products are modeled using constructs of active ingredient, presentation strength, and basis of strength. Since 2018, harmonization of SNOMED CT drug content with IDMP standard is an editorial goal. The following types of entities are present: Medicinal product A higher level term grouping drugs. For example, 398731002 | Product containing sulfamethoxazole and trimethoprim (medicinal product) | Clinical Drug Concept that represents a concrete drug product as used in clinical practice. For example, 317335000 | Product containing precisely esomeprazole 20milligram/1 each conventional release oral tablet (clinical drug)| Dose Form Concept representing how the product is delivered. For example, 385219001 | Conventional release solution for injection (dose form) |. Authoring conventions A goal for SNOMED CT is consistency. Several mechanisms are employed to ensure this. Machine readable concept model is used to check for compliance with a set of rules. Rules for creating fully specified name for a concept define allowed and not allowed patterns. When defining a concept, a proximal primitive parent rule is used (in stated definition) to employ best description logic derived classification of concepts. Separate conventions govern grouping of relationships. Ability to group related relationships is an important strength of SNOMED CT. Rules in Machine Readable Concept Model (MRCM) specify by domain which relationships are never grouped (e.g., 'Is a' or 'Laterality' attributes) and which relationships are always grouped (e.g., 'Finding site'). For correct subsumption inference, some relationships may be