511 research outputs found
a combined top-down and bottom-up approach
The thesis focuses on the interoperability of autonomous legacy databases with
the idea of meeting the actual requirements of an organization. The
interoperability is resolved by combining the topdown and bottom-up
strategies. The legacy objects are extracted from the existing databases
through a database reverse engineering process. The business objects are
defined by both the organization requirements and the integration of the
legacy objects
The Calibration of the HST Kuiper Belt Object Search: Setting the Record Straight
The limiting magnitude of the HST data set used by Cochran et al. (1995) to
detect small objects in the Kuiper belt is reevaluated, and the methods used
are described in detail. It is shown, by implanting artificial objects in the
original HST images, and re-reducing the images using our original algorithm,
that the limiting magnitude of our images (as defined by the 50% detectability
limit) is . This value is statistically the same as the value found in
the original analysis. We find that of the moving Kuiper belt objects
with are detected when trailing losses are included. In the same data
in which these faint objects are detected, we find that the number of false
detections brighter than is less than one per WFPC2 image. We show
that, primarily due to a zero-point calibration error, but partly due to
inadequacies in modeling the HST'S data noise characteristics and Cochran et
al.'s reduction techniques, Brown et al. 1997 underestimate the SNR of objects
in the HST dataset by over a factor of 2, and their conclusions are therefore
invalid.Comment: Accepted to ApJ Letters; 10 pages plus 3 figures, LaTe
Database Engineering Processes with DB-MAIN
Software engineering needs more and more to be supported by CASE tools. Since databases are at the heart of information systems, they deserve a particular attention. More and more CASE tools allow method engineers to implement their own methodology and they allow users to record all their actions, with their rationales, in order to improve the quality of the design and the quality of the documentation of the design. DBMAIN is such a database oriented tool with a method description and a documentation generation facilities. But it has its particularities like its procedural non-deterministic Method Description Language, its well integrated multilevel histories and its userfriendly methodological engine
Plausible home stars of the interstellar object 'Oumuamua found in Gaia DR2
The first detected interstellar object 'Oumuamua that passed within 0.25au of
the Sun on 2017 September 9 was presumably ejected from a stellar system. We
use its newly determined non-Keplerian trajectory together with the
reconstructed Galactic orbits of 7 million stars from Gaia DR2 to identify past
close encounters. Such an "encounter" could reveal the home system from which
'Oumuamua was ejected. The closest encounter, at 0.60pc (0.53-0.67pc, 90%
confidence interval), was with the M2.5 dwarf HIP 3757 at a relative velocity
of 24.7km/s, 1Myr ago. A more distant encounter (1.6pc) but with a lower
encounter (ejection) velocity of 10.7km/s was with the G5 dwarf HD 292249,
3.8Myr ago. Two more stars have encounter distances and velocities intermediate
to these. The encounter parameters are similar across six different
non-gravitational trajectories for 'Oumuamua. Ejection of 'Oumuamua by
scattering from a giant planet in one of the systems is plausible, but requires
a rather unlikely configuration to achieve the high velocities found. A binary
star system is more likely to produce the observed velocities. None of the four
home candidates have published exoplanets or are known to be binaries. Given
that the 7 million stars in Gaia DR2 with 6D phase space information is just a
small fraction of all stars for which we can eventually reconstruct orbits, it
is a priori unlikely that our current search would find 'Oumuamua's home star
system. As 'Oumuamua is expected to pass within 1pc of about 20 stars and brown
dwarfs every Myr, the plausibility of a home system depends also on an
appropriate (low) encounter velocity.Comment: Accepted to The Astronomical Journa
Relational symbolic execution of SQL code for unit testing of database programs
Symbolic execution is a technique enabling the automatic generation of test inputs that exercise a set of execution paths within a code unit to be tested. If the paths cover a sufficient part of the code under test, the test data offer a representative view of the actual behaviour of this code. This notably enables detecting errors and correcting faults. Relational databases are ubiquitous in software, but symbolic execution of code units that manipulate them remains a non-trivial problem, particularly because of the complex structure of such databases and the complex behaviour of SQL statements. Finding errors in such code units is yet critical, as it can avoid corrupting important data. In this work, we define a symbolic execution translating database manipulation code directly into constraints and integrate it with a more traditional symbolic execution of normal program code. The database tables are represented by relational symbols and the SQL statements by relational constraints over these symbols. An algorithm based on these principles is presented for the symbolic execution of simple Java methods that implement transactional use cases by reading and writing in a relational database, the latter subject to data integrity constraints. The algorithm is integrated in a test generation tool and experimented over sample code. The target language for the constraints produced by the tool is the SMT-Lib standard and the used solver is Microsoft Z3. The results show that the proposed approach enables generating meaningful test data, including valid database content, in reasonable time. In particular, the Z3 solver is shown to be more scalable than the Alloy solver, used in our previous work, for solving relational constraints
A Direct Symbolic Execution of SQL Code for Testing of Data-Oriented Applications
Symbolic execution is a technique which enables automatically generating test inputs (and outputs) exercising a set of execution paths within a program to be tested. If the paths cover a sufficient part of the code under test, the test data offer a representative view of the program's actual behaviour, which notably enables detecting errors and correcting faults. Relational databases are ubiquitous in software, but symbolic execution of pieces of code that manipulate them remains a non-trivial problem, particularly because of the complex structure of such databases and the complex behaviour of SQL statements. In this work, we define a direct symbolic execution for database manipulation code and integrate it with a more traditional symbolic execution of normal program code. The database tables are represented by relational symbols and the SQL statements by relational constraints over these symbols and the symbols representing the normal variables of the program. An algorithm based on these principles is presented for the symbolic execution of Java methods that implement business use cases by reading and writing in a relational database, the latter subject to data integrity constraints. The algorithm is integrated in a test generation tool and experimented over sample code. The target language for the constraints produced by the tool is the SMT-Lib standard and the used solver is Microsoft Z3. The results show that the proposed approach enables generating meaningful test data, including valid database content, in reasonable time. In particular, the Z3 solver is shown to be more scalable than the Alloy solver, used in our previous work, for solving relational constraints
Time-Resolved Photometry of Kuiper Belt Objects: Rotations, Shapes and Phase Functions
We present a systematic investigation of the rotational lightcurves of
trans-Neptunian objects based on extensive optical data from Mauna Kea. Four of
13 objects (corresponding to 31%) in our sample ((33128) 1998 BU48, 2000 GN171,
(20000) Varuna and 1999 KR16) were found to exhibit lightcurves with
peak-to-peak range > 0.15 magnitude. In a larger sample obtained by combining
our data with reliably determined lightcurves from the literature, 7 of 22
objects (32%) display significant (> 0.15 magnitude range) lightcurves. About
23% of the sampled objects have lightcurve ranges > 0.4 magnitudes. Curiously,
the objects are very large (> 250 km diameter, assuming an albedo of 0.04) and,
in the absence of rotation, should be near spherical due to self compression.
We propose that the large amplitude, short period objects are rotationally
distorted, low density rubble piles. Statistically, the trans-Neptunian objects
are less spherical than their main-belt asteroid counterparts, indicating a
higher specific angular momentum perhaps resulting from the formation epoch. In
addition to the rotational lightcurves, we measured phase darkening for 7
Kuiper Belt objects in the 0 to 2 degree phase angle range. Unlike Pluto, the
measured values show steep slopes and moderate opposition surge indicating
backscatter from low albedo porous surface materials.Comment: 22 pages, 33 figures, 12 tables, To appear in AJ sept. 200
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