GS1 EPC Tag Data Standard 1.6 - Indicod-Ecr

4020402140224023402440254026402740284029403040314032403340344035403640374038403940404041404240434044404540464047404840494050405140524053405440554056There are two different Packed Objects methods available for representing a sequence ofIdentifiers by reference to their ID Values: An ID List Packed Object (IDLPO) encodes a series of ID Values as a list, whoselength depends on the number of data items being represented; An ID Map Packed Object (IDMPO) instead encodes a fixed-length bit array, whoselength depends on the total number of entries defined in the registered Base Table.Each bit in the array is ‘1’ if the corresponding table entry is represented by thePacked Object, and is ‘0’ otherwise.An ID List is the default Packed Objects format, because it uses fewer bits than an IDMap, if the list contains only a small percentage of the data system’s defined ID Values.However, if the Packed Object includes more than about one-quarter of the definedentries, then an ID Map requires fewer bits. For example, if a data system has sixteenentries, then each ID Value (table index) is a four bit quantity, and a list of four IDValues takes as many bits as would the complete ID Map. An ID Map’s fixed-lengthcharacteristic makes it especially suitable for use in a Directory Packed Object, whichlists all of the Identifiers in all of the Packed Objects in memory (see section I.9). Theoverall structure of a Packed Object is the same, whether an IDLPO or an IDMPO, asshown in Figure I 3-2 and as described in the next subsection.Figure I 3-2 Packed Object StructureOptional Object Info Section Secondary Aux Format Data SectionFormat (IDLPO or IDMPO) ID Section Section (if needed)Flags(if needed) (if needed)Packed Objects may be made “editable”, by adding an optional Addendum subsection tothe end of the Object Info section, which includes a pointer to an “Addendum PackedObject” where additions and/or deletions have been made. One or more such “chains” ofeditable “parent” and “child” Packed Objects may be present within the overall sequenceof Packed Objects in memory, but no more than one chain of Directory Packed Objectsmay be present.I.3.2 Descriptions of each section of a Packed Object’sstructureEach Packed Object consists of several bit-aligned sections (that is, no pad bits betweensections are used), carried in a variable number of octets. All required and optionalPacked Objects formats are encompassed by the following ordered list of Packed Objectssections. Following this list, each Packed Objects section is introduced, and later sectionsof this Annex describe each Packed Objects section in detail. Format Flags: A Packed Object may optionally begin with the pattern ‘0000’ whichis reserved to introduce one or more Format Flags, as described in I.4.2. These flagsmay indicate use of the non-default ID Map format. If the Format Flags are notpresent, then the Packed Object defaults to the ID List format.Copyright ©2005- 2011 GS1 AISBL, All Rights Reserved. Page 165 of 218