MIMEs

The MIME (Multipurpose Internet Mail Extension) type is a two-part identifier for file formats on the Internet. The identifiers were originally defined for use in email, but their use has expanded to various applications including web browsers. They are mainly used to identify media files, such as graphic files (e.g. JPEG, PNG, and GIF) and documents (e.g. PDF, DOC, and XLS). The system uses MIME types to identify files uploaded to the system, for example hazard maps.

Data fields of the MIME records are listed in Table 1.

Table 1. MIME data fields

For each MIME, the type and a descriptive name should be specified. In practice, multiple file types may have the same MIME type (e.g. text/plain). Hence, the type is not necessarily unique. In case of multiple MIME records with the same type value, the system uses user-defined extensions to determine which MIME record to use to represent the file type. In general, the extension is a three-character string com-posed of letters and numbers. The extension should be unique among the MIME records. In shorthand notation, icons are used to represent the MIME type. Therefore, an icon should be specified for each MIME record by making a selection from the provided drop-down list. Icons defined in the common style sheet and having a prefix of "m_" are listed in the icon drop-down list (Figure 1).

Since MIME types are not standardized, different MIME types may refer to the same file type. The selec-tion of the MIME type depends on the client application, which is the web browser of the user for the case of RAPID-N. Currently there are many web browsers available in the market (e.g. Microsoft Internet Explorer, Mozilla Firefox, and Google Chrome) using different MIME types. For example, Microsoft Internet Explorer uses application/pjpeg to denote JPEG images, whereas other browsers use applica-tion/jpeg. In order to standardize such MIME types, equal types are introduced by the system. MIME types, which are defined as the equal types of a MIME type, are automatically converted to the base MIME type. Hence, conflicting MIME types are eliminated in the database. For each MIME type, multiple but unique equal MIME types can be specified (Figure 1).

When a new file is uploaded to the system, its MIME type is extracted from the file information provided by the web browser. If the MIME type is already defined in the database, either as a MIME record or as an "equal type", it is matched to the corresponding MIME record. Otherwise, MIME records are searched for the extension of the uploaded file. If a matching MIME record is found, it is used to identify the file type. If no MIME record is found fulfilling the criteria, a new MIME record is created automati-cally by using the MIME type. The extension of the uploaded file is used as the extension of the MIME type. Its name is generated by converting the extension into upper case and appending "File" to the end in a multilingual manner (e.g. KML File for file.kml). The administrators can modify system-generated MIME records to set an appropriate icon or enter a custom name.