The Application Level Events (ALE) Specification, Version 1.0 - GS1

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348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 • The differential set that only includes differences of the current event cycle relative to the previous one (assuming the same event cycle boundaries). This can be the set of additions R = (Ecur – Eprev) or the set of deletions R = (Eprev – Ecur), where ‘–’ denotes the set difference operator. • An optional filter F(R) to apply, including as part of the standard ALE interface: • One or more object types derived from the “filter bits” of the EPC Tag Data Standard [TDS1.1], including “product” objects (e.g., pallet, case, etc.) as well as “location” objects (e.g., warehouse slots, trucks, retail shelves, etc., that contain embedded EPC tags) • A specific list of EPCs • A range of EPCs • Whether to report • The members of the set, F(R) (i.e., the EPCs themselves), possibly grouped as described in Section 5, and in what format (e.g., pure identity URI, tag URI, raw binary, etc); • The quantity, or cardinality, of the set |F(R)|, or of the groups making up the set as described in Section 5. The available options are described normatively in Section 8.2. A client may require more than one report from a given event cycle; e.g., a smart shelf application may require both an additions report and a deletions report. This all adds up to an ALE Layer API in which the primary interaction involves: (1) a client specifying: (a) one or more Readers (this is done indirectly, as explained in Section 7) (b) event cycle boundaries as enumerated above, and (c) a set of reports as defined above; and (2) the ALE Layer responding by returning the information implied by that report specification for one or more event cycles. This may be done in a “pull” mode, where the client asks for a report or reports (also specifying how the event cycle is to be delimited) and the ALE Layer in turn initiates or waits for read events, filters/counts the data, and returns the report(s). It may also be done in a “push” mode, where the client registers a subscription with a report set and event cycle boundary specification, and thereafter the ALE Layer asynchronously sends reports to the client when event cycles complete. The complete details of the API, the information required to specify an event cycle, and the information returned to the client when an event cycle completes are spelled out in Sections 8.1, 8.2, and 8.3, respectively. Examples of an event cycle specification and event cycle reports in XML are given in Section 10. Note that because the filtering operations commute with the set union and difference operations, there is a great deal of freedom in how an ALE implementation actually carries out the task of fulfilling a report request. For example, in one implementation, there may be a Reader that is capable of doing filtering directly within the Reader, while in a second implementation the Reader may not be capable of filtering and so software implementing the ALE API must do it. But the ALE API itself need not change – the Copyright © 2005, 2004 EPCglobal Inc, All Rights Reserved. Page 12 of 71
388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 client specifies the reports, and the implementation of the API decides where best to carry out the requested filtering. 5 Group Reports Sometimes it is useful to group EPCs read during an event cycle based on portions of the EPC or attributes of the objects identified by the EPCs. For example, in a shipment receipt verification application, it is useful to know the quantity of each type of case (i.e., each distinct case GTIN), but not necessarily the serial number of each case. This requires slightly more complex processing, based on the notion of a grouping operator. A grouping operator is a function G that maps an EPC code into some sort of group code g. For example, a grouping operator might map an EPC code into a GTIN group, or simply into the upper bits (manufacturer and product) of the EPC. Other grouping operators might be based on other information available on an EPC tag, such as the filter code that implies the type of object (i.e., pallet, case, item, etc.). The notation S↓g means the subset of EPCs s1, s2, … in the set S that belong to group g. That is, S↓g ≡ { s in S | G(s) = g }. A group membership report for grouping operator G is a set of pairs, where the first element in each pair is a group name g, and the second element is the list of EPCs that fall into that group, i.e., S↓g. A group cardinality report is similar, but instead of enumerating the EPCs in each group, the group cardinality report just reports how many of each there are. That is, the group cardinality report for grouping operator G is a set of pairs, where the first element in each pair is a group name g, and the second element is the number of EPCs that fall into that group, i.e., |S↓g|. Formally, then, the reporting options from the last section are: • Whether to report • A group membership (group list) report for one or more specified grouping operators Gi, which may include, and may possibly be limited to, the default (unnamed) group. In mathematical notation: { (g, F(R)↓g) | F(R)↓g is non-empty }. • A group cardinality (group count) report for one or more specified grouping operators Gi, which may include, and may possibly be limited to, the default (unnamed) group. In mathematical notation: { (g, |F(R)↓g|) | F(R)↓g is nonempty }. 6 Read Cycle Timing The ALE API is intentionally silent about the timing of read cycles. Clients may specify the boundaries of event cycles, which accumulate data from one or more underlying read cycles, but the API does not provide a client with explicit control over the frequency at which read cycles are completed. There are several reasons for this: Copyright © 2005, 2004 EPCglobal Inc, All Rights Reserved. Page 13 of 71
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The Application Level Events (ALE) Specification, Version 1.0 - GS1

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