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Variable and state handling in NCL

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Abstract

Most time-based declarative languages have limited support for variable definition and manipulation, which causes developers to resort to imperative languages. However, a declarative language should provide a variable handling model sufficiently rich to describe a wide range of interactive applications, avoiding, as much as possible, the help of an imperative scripting language. On the other hand, the declarative simplicity should not be lost, leaving for the imperative objects more complex manipulations, with the necessary care to avoid any impact in the application’s temporal graph. Based on this principle, variables and the presentation state are handled by NCL and Ginga-NCL, as discussed in this paper. NCL is the declarative language of the Brazilian Terrestrial Digital TV System (SBTVD) supported by its middleware called Ginga. NCL and Ginga-NCL are part of ISDB standards and also of ITU-T Recommendations for IPTV services.

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Notes

  1. In NCL, variables are called properties. In the remainder of this document, the terms variable and property will be used interchangeably when referring to NCL variables.

  2. In DTV systems, it is usual to have DSM-CC stream events triggering the execution of imperative codes.

  3. SMIL uses the term “state variable” instead of “global variable”.

  4. The attribute of a element specifies the location for retrieving the media object’s content. The attribute specifies how the media object must be presented.

  5. The element represents the same animation video (attribute ) that is specified by the element (attribute ).

  6. Reserved variables are the ones whose name and semantics are defined in the NCL profile specification [1, 10].

  7. Lua is the Ginga scripting language, while Xlet is the Java code that runs in Ginga.

  8. Transition effects are defined in NCL by elements, and referred by elements through its and attributes.

  9. For the Brazilian DTV System, the NCL profile only allows causal relationships.

  10. In the case of XML languages, XSL transformations can be applied to document trees.

References

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  2. ARIB Association of Radio Industries and Business (2004) ARIB Standard B-24 Data Coding and Transmission Specifications for Digital Broadcasting, version 4.0, 2004

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Acknowledgments

The authors would like to thank Carlos Salles, Romualdo Costa, Marcio Moreno, Marcelo Moreno and Francisco Sant’anna who provided thoughtful discussion of this work, and tracked down and fixed problems in the initial reference implementation of Ginga. The authors also thank Ethan Munson for his careful revision of the paper, and CNPq, FINEP and FAPERJ for their support.

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Authors and Affiliations

  1. Pontifícia Universidade Católica do Rio de Janeiro, Rua Marquês de São Vicente 225, 22451-900, Rio de Janeiro, RJ, Brazil

    Luiz Fernando G. Soares, Rogério Ferreira Rodrigues, Renato Cerqueira & Simone Diniz Junqueira Barbosa

  2. Microsoft® Corporation/FAST, a Microsoft® Subsidiary, Av. Rio Branco 1, 1611, 20090-003, Rio de Janeiro, RJ, Brazil

    Rogério Ferreira Rodrigues

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  1. Luiz Fernando G. Soares
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  2. Rogério Ferreira Rodrigues
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Correspondence to Luiz Fernando G. Soares.

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Soares, L.F.G., Rodrigues, R.F., Cerqueira, R. et al. Variable and state handling in NCL. Multimed Tools Appl 50, 465–489 (2010). https://doi.org/10.1007/s11042-010-0478-2

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