2.1.6 Ascii Art
Francisco Raya
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This OGC Encoding Standard defines GeoPackages for exchange and GeoPackage SQLite Extensions for direct use of vector geospatial features and / or tile matrix sets of earth images and raster maps at various scales. Direct use means the ability to access and update data in a "native" storage format without intermediate format translations in an environment (e.g., through an API) that guarantees data model and data set integrity and identical access and update results in response to identical requests from different client applications. GeoPackages are interoperable across all enterprise and personal computing environments, and are particularly useful on mobile devices like cell phones and tablets in communications environments with limited connectivity and bandwidth.
A GeoPackage is an open, standards-based, platform-independent, portable, self-describing, compact format for transferring geospatial information.It is a platform-independent SQLite [I5] database file that contains the GeoPackage data and metadata tables shown in Figure 1 below.
These conventions include table definitions, integrity assertions, format limitations, and content constraints. The required and supported content of a GeoPackage is entirely defined in the standard. These capabilities are built on a common base and the extension mechanism provides implementors a way to include additional functionality in their GeoPackages.
Since a GeoPackage is a database container, it supports direct use. This means that the data in a GeoPackage can be accessed and updated in a "native" storage format without intermediate format translations. GeoPackages that comply with the requirements in the standard and do not implement vendor-specific extensions are interoperable across all enterprise and personal computing environments. GeoPackages are particularly useful on mobile devices such as cell phones and tablets in communications environments where there is limited connectivity and bandwidth.Mobile device users who require map/geospatial application services and operate in disconnected or limited network connectivity environments are challenged by limited storage capacity and the lack of open format geospatial data to support these applications.
This standard is intended to facilitate widespread adoption and use of GeoPackages by both COTS and open-source software applications on enterprise production platforms as well as mobile hand-held devices [B1] [B2], given that mobile hand held devices do not yet have the processing power or battery life to effectively tackle difficult geospatial product production and analysis tasks.
An Extended GeoPackage is a GeoPackage that contains any additional data elements (tables or columns) or SQL constructs (views, data types, functions, indexes, constraints or triggers) that are not automatically maintained within the SQLite data file or that result in a change in behavior not specified in this encoding standard.
A GeoPackage MAY be "empty" (contain user data table(s) for vector features, non-spatial attributes, and/or tile matrix pyramids with no row record content) or contain one or many vector feature type records and /or one or many tile matrix pyramid tile images.GeoPackage metadata CAN describe GeoPackage data contents and identify external data synchronization sources and targets.A GeoPackage MAY contain spatial indexes on feature geometries and SQL triggers to maintain indexes and enforce content constraints.
A GeoPackage SQLite Extension is a SQLite loadable extension that MAY provide SQL functions [I12] to support spatial indexes and SQL triggers linked to a SQLite library with specified configuration requirements to provide SQL API [I1] [I2] [I3] [I4] access to a GeoPackage file. This standard does not address the issues listed in the Potential Future Work (Informative) clause in Background and Context (Normative), which MAY be addressed in a subsequent version of this standard or by other specifications.
The required capabilities specified in this clause serve as the base for options specified in clause Options and extensions specified in clause Registered Extensions (Normative).All gpkg_* tables and views and all tiles user data tables specified in this standard SHALL have only the specified columns and table constraints. Any features user data tables MAY have columns in addition to those specified.All table, view, column, trigger, and constraint name values specified in this standard are lowercase.
SQLite is more flexible with regards to identifiers than many other RDBMS systems.If GeoPackage data is to be used in other RDBMS systems, standard practices SHOULD be used to reduce potential interoperability risks.For maximum interoperability, all user-defined GeoPackage table, view, column, trigger, and constraint name values SHOULD start with a lowercase character and only include lowercase characters, numbers 0-9, and underscores (_).In addition, some RDBMS systems truncate identifier names that are longer than a fixed byte length which may be as short as 30 bytes.Therefore, long GeoPackage identifier values SHOULD be avoided and if long identifier values are used, then they SHOULD be unique for at least the first 30 bytes.
The mandatory core capabilities defined in sub clauses and requirement statements of this clause SHALL be implemented by every GeoPackage and GeoPackage SQLite Configuration.
The SQLite software library provides a self-contained, single-file, cross-platform, serverless, transactional, open source RDBMS container.The GeoPackage standard defines a SQL database schema designed for use with the SQLite software library.Using SQLite as the basis for GeoPackage simplifies production, distribution and use of GeoPackages and assists in guaranteeing the integrity of the data they contain.
"Self-contained" means that container software requires very minimal support from external libraries or from the operating system."Single-file" means that a container not currently opened by any software application consists of a single file in a file system supported by a computing platform operating system."Cross-platform" means that a container file MAY be created and loaded with data on one computing platform, and used and updated on another, even if they use different operating systems, file systems, and byte order (endian) conventions."Serverless" means that the RDBMS container is implemented without any intermediary server process, and accessed directly by application software."Transactional" means that RDBMS transactions guarantee that all changes to data in the container are Atomic, Consistent, Isolated, and Durable (ACID) despite program crashes, operating system crashes, and power failures.
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