Open Packaging Convention standard applied to compressed hypermaps

Open Packaging Convention standard applied to compressed hypermaps

The OPC standard

OPC (also known as OOXML) is a packaging strategy  that integrates elements of the ZIP compression, XML documents, and the web MIME types into an open standard that makes it easier to organize, store, and transport data. It was defined by Microsoft and approved as ISO 29500-2 and ECMA-376. It is used by Office 2007 and newer versions of Word (.docx), Excel (.xlsx), and PowerPoint (.pptx), along with XPS (.xps), Autodesk AutoCAD (.dwfx), etc (Figure 1). An OPC package can contain several files with a directory structure in it. Each file is called a “part” and all OPC package part names have to follow the URI restrictions and conventions. The format adds some extra files to increase interoperability. It incorporates a standardized way of recording file relations or links. It also incorporates a file with a few elements of metadata and a thumbnail with a small image for presentation purposes. All these extra parts allow some basic independent data maintenance, such as the extraction of a fragment of the package, thus guaranteeing that all the related resources will be extracted without the need to understand the actual encoding of the parts included in the package.

OPC is conceptually very similar to the KMZ and MMZ format, but offers some advantages. KMZ is a compressed file that uses a ZIP file format following the solution reuse criteria, but its structure is deeply related to the original KML. Therefore, it does not comply with the completeness criteria, and KMZ strategy is not accurately documented (it is not included in the KML specification) and thus, it does not comply with the formality and metamodel identity criteria. MMZ was never submitted for standardization or adopted by other vendors and has not reached a high popularity outside the GIS community. OPC uses an accepted popular compression schema and header (ZIP compression) but combines other advantages such as it can be directly manipulated by other OPC compatible tools that recognize the file structure and relations even if they are not able to identify or understand the format of some compressed parts. Phillips and Allemang (2010) prefer it over other alternatives as a file format for data archiving.

How to apply it to geospatial information

OPC format offers an opportunity for designing an standardized way to pack geospatial information in a single file that internally used the original data files that can be later recovered as they were produced. Due to the similarities between the old MMZ format and the OPC standard, we call this approach MMZX. Most GIS software offer the capability save a session composed by different information layers, symbolization, presentation, metadata, etc. This format does not contains the information but links to it. Recently the OGC has introduced a new standardized format that also can to this: the OWS context. It is possible to create a software that is able to collect the "context" file plus all the data files and symbolization and configuration files and create a OPC package. Apart from the geospatial data parts of the file, OPC specifies how to explicitly relate different parts using .rels files (relations are composed of a source file and a target file, and the purpose of this relation is like in the RDF format). These files are XML files that have the same name as that of its respective source part adding “.rels” and placed in a “rels” folder. Each of these files lists the target parts related to its source and the semantics of this relation. 

MiraMon implementation

Recently, MiraMon has complemented the old MMZ file with the new MMZX file format that is fully follows to the OPC standard. This format is able to share geospatial information in a single file that can be decompressed and visualize automatically using the MiraMon Universal Map Reader (http://miramon-universal-map-reader.en.softonic.com/) or the MiraMon professional software

How to read and see the internal OPC structure

This page provides some clues on how to work ith OPC files http://www.wikihow.com/Open-XML. Mainly, there are two general use tools for doing this the Package Explore and the OOXML Chrome viewer plug-in.

More information about the OPC format

• Wikipedia page
• Good description of the format structure
• ISO/IEC 29500-2:2012, specification document
• Very good page form the library of the congress with link to more resources
• LibOPC