Fast and Tiny Structural Self-Indexes for XML

XML document markup is highly repetitive and therefore well compressible using dictionary-based methods such as DAGs or grammars. In the context of selectivity estimation, grammar-compressed trees were used before as synopsis for structural XPath queries. Here a fully-fledged index over such grammars is presented. The index allows to execute arbitrary tree algorithms with a slow-down that is comparable to the space improvement. More interestingly, certain algorithms execute much faster over the index (because no decompression occurs). E.g., for structural XPath count queries, evaluating over the index is faster than previous XPath implementations, often by two orders of magnitude. The index also allows to serialize XML results (including texts) faster than previous systems, by a factor of ca. 2-3. This is due to efficient copy handling of grammar repetitions, and because materialization is totally avoided. In order to compare with twig join implementations, we implemented a materializer which writes out pre-order numbers of result nodes, and show its competitiveness.Comment: 13 page

Legal, compliant and suitable: The ECB‘s Pandemic Emergency Purchase Programme (PEPP).BertelsmannStiftung/jacques Delors Centre Policy Brief 25 March 2020

The ECB has announced a 750-billion-euro purchase programme to fight the economic impact of the COVID-19 pandemic. But like all ECB programmes in recent years, the new Pandemic Emergency Purchase Programme (PEPP) will likely be challenged in court. This policy brief assesses whether the PEPP will likely survive a legal challenge. It argues that the PEPP is compatible with EU law because it meets the three criteria the Court of Justice of the EU has established to check the legality of monetary policy measures: First, the PEPP falls within the ECB’s mandate. Second, it respects the principle of proportionality. And third, it does not violate the prohibition of monetary financing. This assessment even holds if the ECB were to relax some of the constraints in the PEPP like the issuer limit currently applicable to other bond-buying programmes

Can Representationism Explain how Attention Affects Appearances?

Recent psychological research shows that attention affects appearances. An “attended item looks bigger, faster, earlier, more saturated, stripier.” (Block 2010, p. 41). What is the significance of these findings? Ned Block has argued that they undermine representationism, roughly the view that the phenomenal character of perception is determined by its representational content. My first goal in this paper is to show that Block’s argument has the structure of a Problem of Arbitrary Phenomenal Variation and that it improves on other instances of arguments of the same form along several dimensions (most prominently, these are arguments based on the possibility of spectral inversion). My second goal is to consider responses to Block’s version of the arbitrariness problem. I will show that most of them have serious drawbacks. Overall, the best view is to accept that attention may distort perception, sacrificing veridicality for usability. I end my discussion by showing how to develop that view

Ineffability: The very concept

In this paper, I analyze the concept of ineffability: what does it mean to say that something cannot be said? I begin by distinguishing ineffability from paradox: if something cannot be said truly or without contradiction, this is not an instance of ineffability. Next, I distinguish two different meanings of ‘saying something’ which result from a fundamental ambiguity in the term ‘language’, viz. language as a system of symbols and language as a medium of communication. Accordingly, ‘ineffability’ is ambiguous, too, and we should make a distinction between weak and strong ineffability. Weak ineffability is rooted in the deficiencies of a particular language while strong ineffability stems from the structure of a particular cognitive system and its capacities for conceptual mental representation. Mental contents are only sayable if we are able to conceptualize them and then create signs to represent them in communication