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The file naming convention specified in this section applies to all SNOMED International release files starting with the January 2010 International release.

The specification provides the following benefits:

  • A consistent naming convention across the International edition and each National edition.

  • Predictable file naming, providing a stable structure for naming over time between releases.
  • A standard way to identify the source country and namespace by which a release file is owned.

  • A consistent versioning mechanism.
  • An easy human readable way to identify the content of a file, at a summary level.
  • A mechanism for identifying the type of information stored in a release file(e.g. documentation, tooling, etc.).

  • Guidance on file naming for release files in non-English extensions.

  • Assurance that names will be unique across the International release and releases from individual National release centers and across separate releases from each center over time.

  • An upgrade path, to enable use of the same naming convention with the new release format( RF2), while enabling easy identification of whether a file is in RF1 or RF2 format, and avoiding naming clashes.

Quality Assurance checks, to ensure that this naming convention is enforced, will be performed as part of the International release process. It is expected that equivalent checks will be performed as part of each National Release Center 's release process.

Note: Prior to January 2010 other naming strategies were used. Implementers who need to review earlier releases should consult the documentation that accompanied the release that they need to review.

File Naming Convention - Overview

General File Naming Pattern

The basic pattern for SNOMED CT release file names consists of five elements, each separated by an underscore (" _ ") and followed by a full stop (" . ") and a file extension:

<FileType><ContentType><ContentSubType><Country|Namespace><VersionDate>.<Extension>

Each element in the above structure is described in more detail in subsequent sections.

General Naming Rules

The following rules apply generally to all elements of the file name:

  • All elements are mandatory and may not have a null value;
  • Elements of the file name may only contain alphanumeric characters, with the exception of hyphens (" - ") used in connection with language codes (see detail for the ContentSubType element below);

  • All text should be in US English, except as explicitly allowed below;
  • Abbreviations should not be used, except for specified codes or tags;
  • The maximum length of a file name (including separators and extension) is 128 characters.

Rules for "Readme" Files

Readme files distributed as part of a SNOMED CT release have their own specific naming convention, as shown below: Language is the language code for the language of the Readme file, as specified below for the ContentSubType element, and the VersionDate corresponds to the version date of the release.

FileType Element

Description

The FileType element of the filename designates the type and intended use of the release file. It consists of a 3-5 letter code and must be lowercase.

Rules

Allowable FileType codes are shown in the table below:

Table 2.1-1: Allowable File Type Codes

Code

File Type Description 

"sct" + <format tag>

Terminology Data File

"der" + <format tag>

Derivative Work Data File

"res" (+ <format tag>)

Implementation Resource Data File

"tls" (+<format tag>)

Implementation Resource Tool

"doc" (+<format tag>)

Documentation

"z" + Code

Archival/Unsupported File (e.g. zsct)

"x" + Code

Test/Beta Release File (e.g. xder)

The allowable file types are described in more detail below:

  • Terminology Data File (" sct ") - the set of data files that make up the SNOMED CT terminology. These are:

  • Derivative Work Data File (" der ") - data files that make up a SNOMED CT" derivative work" (a product for use in conjunction with SNOMED CT that cannot be effectively used without the terminology - such as subsets or maps). Examples of the files within this group include:

  • Implementation Resource Data File (" res ") - data files intended to support developers with the implementation of SNOMED CT, but that are not necessarily useful to end-users. Examples from the current International Release include:

  • Implementation Resource Tool (" tls ") - software tools or other files that do not contain original SNOMED CT content (i.e. that is not also held elsewhere in the release), but can be of use to implementers. If such files cannot comply with this naming convention (for example, if some other standard applies), then those files should be distributed as part of a ZIP file archive that does conform to this file naming convention.

  • Documentation (" doc ") - documents defining SNOMED CT standards, policies and guidelines, as well as documentation for files or products included in a SNOMED CT release. Most, but not all, files in this group are released in a PDF format.

  • Archival/Unsupported File (" zsct ", " zder ", " zres ", " ztls ") - files that are not currently supported or updated, but may be of some use to implementers. These files should only be used with caution and after appropriate review and validation. The letter " z " is inserted in front of the usual FileType code for these files (i.e. " z " + " sct ", " der ", " res " or " tls "). Examples from the current International Release include:

  • Test/Beta Release File(" xsct ", " xder ", " xres ", " xtls ") - files distributed as part of a test/beta release, or as a "technology preview". These files should only be used for review and evaluation purposes. The letter " x " is inserted in front of the usual FileType code for these files (i.e. " x " + " sct ", " der ", " res " or " tls ").

Format Tags

A Release Format tag must be appended at the end of the three-letter FileType code if the file named is dependent on a particular Release Format specification. The allowable Release Format tags are:

  • For files that are part of the current Release Format( RF2), or applicable only to the RF2 Release Format, the number " 2 " is appended to the FileType code (e.g. " sct2 ", " der2 ", " res2 ").

  • For files that are part of the now obsolete RF1 Release Format, or applicable only to that Release Format, the number " 1 " is appended to the FileType code (e.g. " sct1 ", " der1 ", " tls1 ").

  • If the file is not specific to either Release Format, the three-letter FileType code should be used without a Release Format tag (e.g. " res ", " tls " or " doc ").

  • The FileType code for all terminology and Derivative Work data files (" sct " or " der ") must include a Release Format tag (" 1 " or " 2 "). For other file types, the Release Format tag is optional.

ContentType Element

Description

The ContentType element of the filename describes the content and purpose of the file. It consists of 2-48 alphanumeric characters in camel case.

Rules

The content of this element depends on the first element (FileType) of the filename, as described below:

Possible values for the Release Format 2 are:

For Data files where the ContentType element is " Refset", the ContentType element will also describe the format and content of the reference set member file. Each file of ContentType " Refset" will hold zero or more additional columns, each having one of the following types:

Lower case " c ", " s " and " i " will be used as abbreviations (for component, String and Integer respectively) to describe the format of the additional columns that will be appended to the end of each row in the Refset file. These abbreviations will prefix the ContentType element, as shown in the examples below:

  • cRefset - a Refset file with one additional column, holding component values;

  • ssRefset - a Refset file with two additional columns, both holding String values;

  • ciRefset - a Refset file also with two additional columns, the first holding component values and the second holding Integer values;

  • For ImplementationResource Tools (" tls ") - the value of the ContentType element may be determined on a case-by-case basis but, in conjunction with the ContentSubType element, should be adequate to identify the content and purpose of the file;
  • For Documentation (" doc ") - the title of the document, which may be abridged but should not be abbreviated, should be used as the value for the ContentType element;
  • For Archival & Test/Beta Files (" z "+ code or " x "+ code) - the value of the ContentType element should be determined according to the rules for a normal file of the same type (" sct ", " der ", " res " or " tls ").

ContentSubType Element

Description

The ContentSubType element of the filename provides additional information to describe the content and purpose of the file, including the language/ dialect, where appropriate. Its format is 2-48 alphanumeric characters in camel case (except for the capitalization rules specified below for language code). Hyphen (" - ") is a permitted character in conjunction with a language code, as described below.

Rules

The content of this element depends on the first element type (FileType), and these rules are described in more detail below:

  • Data Files (" sct ", " der " or " res ") - as a result of RF2's state-valid history tracking capability, it is possible to perform a number of different releases of SNOMED CT content in the RF2 format:

    • A " Full " release of each file containing every version of every component ever released.
    • A " Snapshot " release, containing only the most recent version of every component ever released (both active and inactive components).

    • A " Delta " release, containing only component versions created since the last release. Each component version represents a new component or a change in an existing component.

Each RF2 ContentSubType element must be postfixed with a Release Type flag with a value of: " Full ", " Snapshot " or " Delta ". This flag should always appear at the end of the ContentSubType element, unless ContentSubType includes a language code (see below). If a language code is present in the ContentSubType element, the Release Type flag will appear immediately before the language code.

  • Implementation Resource Tool (" tls ") - the value of this element may be determined on a case-by-case basis but, in conjunction with the ContentType element, should be adequate to identify the content and purpose of the file. If appropriate, the element may contain a status tag with one of the values described below under Documentation.
  • Documentation (" doc ") - the element should contain at least two components: a status tag and a language code (see above). Additional components may be added to this element if necessary to fully identify the document. Possible values for the document status tag are:

    • " Current " - indicates that the document is up-to-date and complete for the current release of SNOMED CT, as indicated by the VersionDate element;

    • " Draft " - indicates that the document is a draft version; it may be incomplete and has not been approved in a final version;
    • " Review " - indicates that the document has been released for review and comments from SNOMED CT users and other stakeholders.

  • Archival & Test/Beta File (" z "+ code or " x "+ code) - the value of the element should be determined according to the rules for a normal file of the same type (" sct ", " der ", " res " or " tls ").

Language Usage

For files released as part of a National or local release, and which do not appear in the SNOMED CT International Release, the value of the ContentSubType element may be given in a language other than English, with the following limitation:

  • Any of the four sets of defined values for the ContentSubType element that are present in the file name may not be translated, but must appear as specified herein. These are: language code, Release Type flags (" Full ", " Snapshot ", " Delta "), placeholders (" Core ", " National ", " Local "), and status tags (" Current ", " Draft ", " Review ").

Language Codes

Where it is necessary to specify the language of a file, a language code must be included in the ContentSubType element. A language code is a string identifying the language and, if appropriate, the dialect of a file, and consists of a code and optionally a sub-code. If a sub-code is present it is separated from the code by a hyphen (" - ").

The code is the two-character ISO 639-1 language code. ISO 639 is the International Standard for "Codes for the representation of names of languages". The sub code is a string of upper-case letters that represent the dialect. This deliberately mirrors the W3C approach and will either be:

  • If the dialect is general to an entire country, the two-letter ISO 3166 country code is used. ISO 3166 is the International Standard for "Codes for the representation of names of countries".

  • If dialects are used that are less common or not country or language linked, the IANA approach is used; this code consists of a string of more than two letters. IANA is the Internet Assigned Numbers Authority.

This structure follows Internet conventions. Examples: " en " for English, " es " for Spanish, " en-US " for United States English, " en-GB " for British English.

If the ContentSubType includes more than one component (e.g. document status and a language code), the language code must be the last component in theContentSubType element and should be preceded by a hyphen (" - ") placed before the language code.

Country|Namespace Element

Description

The Country | Namespace element of the filename helps to identify the organization responsible for developing and maintaining the file. Its format is 2-10 alphanumeric characters consisting of 0, 2 or 3 upper-case letters followed by 0 or 7 digits.

Rules

The following rules apply to the content of this element:

Valid combinations are:

VersionDate Element

Description

The VersionDate element of the filename identifies the SNOMED CT version with which the file is intended to be used. Its format is an 8-digit number in the pattern "YYYYMMDD", in compliance with the ISO 8601 standard.

Rules

The following rules apply to the content of this element:

  • For Data Files(" sct "," der " or " res "),and for Documentation (" doc ") with a status tag value of " Current ", the value of this element should always be the same as the SNOMED CT version date with which the file is associated.

  • For other file types, the VersionDate element will identify the (past) date of the SNOMED CT release for which the file was intended. A file distributed with a past version date has not been updated to reflect changes to SNOMED CT since that date, nor has it been validated as correct or appropriate for current use.

VersionDate refers to the official, published date of a SNOMED CT International Release, or of the National Release of an Member country, and may not always correspond to the actual date of distribution of any particular release.

Extension Element

The extension element of the filename identifies the file format (encoding convention) of the file, such as " txt ", " pdf " or " zip ". It has a format of 1-4 alphanumeric characters.


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