Transcript Databases Meet Astronomy a db view of astronomy

Four Talks
Jim Gray, Microsoft
Alex Szalay, Ani Thakar, Jan Vandenberg, JHU
Chris Stoughton, Fermilab
• The article we actually wrote
Online Scientific Publication, Curation, Archiving
• The advertised talk
Computer Science Challenges in the VO
• A Web Server (SkyServer) tour
• A Web Service (SdssCutout) tour
• These lead up to Alex Szalay’s talk on Web Services
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The Paper We Wrote
Online Scientific
Publication, Curation, Archiving
Jim Gray, Microsoft
Alex Szalay, Ani Thakar, Jan Vandenberg, JHU
Chris Stoughton, Fermilab
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Premise
• Once published,
scientific data needs to be available forever,
so that the science can be reproduced/extended.
• What does that mean?
– Data
• Ephemeral Data: could not be reproduced
• Stable data: could be drived from emphemeral data.
– Meta-data: how the data was collected/derived
is ephemeral
• Must be preserved
• Includes design docs, software, email, pubs, personal notes
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Publishing Data
Roles
Traditional
Emerging
Authors
Scientists
Collaborations
Publishers
Journals
Project web site
Curators
Libraries
Data+Doc Archives
Archives
Archives
Digital Archives
Consumers Scientists
Scientists
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The Core Problem: No Economic Model
• The archive user has not yet been born.
How can he pay you to curate the data?
• The Scientist gathered data for his own purpose
Why should he pay (invest time) for your needs?
• Answer to both:
that’s the scientific method
• Curating data
(documenting the design, the acquisition and the processing)
Is very hard and there is no reward for doing it.
The results are rewarded, not the process of getting them.
• Storage/archive NOT the problem (it’s almost free)
• Curating/Publishing is expensive.
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What SDSS is Doing: Capture the Bits
• Best-effort documenting data and process.
• Publishing data: often by UPS
(~ 5TB today (dr1) and so ~15k$ for a copy)
• Replicating data on 3 continents.
• EVERYTHING online (tape data is dead data)
• Archiving all email, discussions, ….
• Keeping all web-logs.
• Now we need to figure out how to
organize/search all this metadata.
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SDSS Data Inflation – Data Pyramid
• Level 1A
Grows 5TB pixels/year
growing to 25TB
~ 2 TB/y compressed
growing to 13TB
~ 4 TB today
(level 1A in NASA terms)
• Level 2
Derived data products ~10x smaller
But there are many catalogs.
• Publish new edition each year
– Fixes bugs in data.
– Must preserve old editions
– Creates data pyramid
• Store each edition
– 1, 2, 3, 4… N ~ N2 bytes
• Net: Data Inflation: L2 ≥ L1
Level 1A
4 editions of Level 2 products
E4
E3
time
E2
E1
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Summary
• Virtual Observatory will be an ecosystem of
authors, curators, publishers, archivers, readers
contributing & using shared data.
• The process and roles are changing
author + project = publisher + curator
• Ephemeral & stable data
Capture ephemeral information.
All design & metadata info is ephemeral
Can tradeoff recomputing derived data
• Economics
Author/Curate cost dominates
• SDSS
Data Inflation, Data Pyramid
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Four Talks
• The article we actually wrote
Online Scientific Publication, Curation, Archiving
• The advertised talk
Computer Science Challenges in the VO
• A Web Server (SkyServer) tour
• A Web Service (SdssCutout) tour
• These lead up to Alex Szalay’s talk on Web Services
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The Advertised Talk
Computer Science Challenges
in the VO
Jim Gray, Microsoft
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Virtual Observatory
• Premise: Most data is (or could be online)
• So, the Internet is the world’s best telescope:
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It has data on every part of the sky
In every measured spectral band: optical, x-ray, radio..
As deep as the best instruments (2 years ago).
It is up when you are up.
The “seeing” is always great
(no working at night, no clouds no moons no..).
– It’s a smart telescope:
links objects and data to literature on them.
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Virtual Observatory
Data Federation of Web Services
• Massive datasets live near their owners:
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Near the instrument’s software pipeline
Near the applications
Near data knowledge and curation
Computer centers become Data Centers
• Archives are replicated for
– Performance
– Availability/Reliability
• Each Archive publishes a web service
– Schema: documents the data
– Methods on objects (queries)
• Scientists get “personalized” extracts
• Uniform access to multiple Archives
– A common global schema
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Some Unique Things About Astro Data
• There is a desire to compare data from different instruments
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Most astronomers publish their data (especially surveys)
Combining data from different instruments gives more info
Szalay observes Metcalf’s law: utility grows as N2
This is less true in some other fields
• It’s tractable
– sizes fit in current regimes (10s of terabytes today)
– tasks fit Beowulfs
• Astro data is great sandbox for CS research.
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High-dimensional data
Temporal, spatial, image datatypes
Few privacy/commercial concerns
There is lots of it
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My #1 Challenge: going beyond files
(a file is an array of bytes)
Science
vs Commerce
• Data in files
•
FTP a local copy /subset.
ASCII or Binary.
• Each scientist builds own •
analysis toolkit
• Analysis is tcl script of •
toolkit on local data.
• Some simple visualization •
tools: x vs y
Data in a database
Standard reports for
standard things.
Report writers for
non-standard things
GUI tools to explore data.
– Decision trees
– Clustering
– Anomaly finders
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But…some science is hitting a wall
FTP and GREP are not adequate
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You can GREP 1 MB in a second
You can GREP 1 GB in a minute
You can GREP 1 TB in 2 days
You can GREP 1 PB in 3 years.
•
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You can FTP 1 MB in 1 sec
You can FTP 1 GB / min (= 1 $/GB)
…
2 days and 1K$
…
3 years and 1M$
• Oh!, and 1PB ~10,000 disks
• At some point you need
indices to limit search
parallel data search and analysis
search and analysis tools
• This is where databases can help
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What’s needed?
(not drawn to scale)
Miners
Scientists
Science Data
& Questions
Data Mining
Algorithms
Plumbers
Database
To store data
Execute
Queries
Question &
Answer
Visualization
Tools
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Scientists
Science Data
& Questions
CS Challenges For Astronomers
• Objectify your field:
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Precisely define what you are talking about.
Objects and Methods / Attributes
This is REALLY difficult.
UCDs are a great start but, there is a long way to go
• “Software is like entropy, it always increases.”
-- Norman Augustine, Augustine’s Laws
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Beware of legacy software – cost can eat you alive
Share software where possible.
Use standard software where possible.
Expect it will cost you 25% to 40% of project. 
• Explain what you want to do with the VO
– 20 queries or something like that.
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Data
Mining
Algorithm
s
Miners
Challenge to Data Miners:
Linear and Sub-Linear Algorithms
Techniques
• Today most correlation / clustering algorithms
are polynomial N2 or N3 or…
• N2 is VERY big when N is big (1018 is big)
• Need sub-linear algorithms
• Current approaches are near optimal
given current assumptions.
• So, need new assumptions
probably heuristic and approximate
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Data
Mining
Algorithm
s
Miners
Challenge to Data Miners:
Rediscover Astronomy
• Astronomy needs deep
understanding of physics.
• But, some was discovered
as variable correlations
then “explained” with physics.
• Famous example:
Hertzsprung-Russell Diagram
star luminosity vs color (=temperature)
• Challenge 1 (the student test):
How much of astronomy can data mining discover?
• Challenge 2 (the Turing test):
Can data mining discover NEW correlations?
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Plumbers
Database
To store
data
Execute
Queries
Plumbers:
Organize and Search Petabytes
• Automate
– instrument-to-archive pipelines
It is is a messy business – very labor intensive
Most current designs do not scale (too many manual steps)
BaBar (1TB/day) and ESO pipeline seem promising.
A job-scheduling or workflow system
– Physical Database design & access
• Data access patterns are difficult to anticipate
• Aggressively and automatically use indexing, sub-setting.
• Search in parallel
• Goals
– Answer easy queries in 10 seconds.
– Answer hard queries (correlations) in 10 minutes.
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Q: How can a computer scientist help,
without learning a LOT of Astronomy?
A: Scenario Design: 20 questions.
• Astronomers proposed 20 questions
Typical of things they want to do
Each would require a week (or month) of
programming in tcl / C++/ FTP
• Goal, make it easy to answer questions
• DB and tools design motivated by this goal
– Implemented DB & utility procedures
– JHU Built GUI for Linux clients
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The 20 Queries
Q1: Find all galaxies without unsaturated pixels within 1' of a given
point of ra=75.327, dec=21.023
Q2: Find all galaxies with blue surface brightness between and 23
and 25 mag per square arcseconds, and -10<super galactic
latitude (sgb) <10, and declination less than zero.
Q3: Find all galaxies brighter than magnitude 22, where the local
extinction is >0.75.
Q4: Find galaxies with an isophotal surface brightness (SB) larger
than 24 in the red band, with an ellipticity>0.5, and with the
major axis of the ellipse having a declination of between 30”
and 60”arc seconds.
Q5: Find all galaxies with a deVaucouleours profile (r¼ falloff of
intensity on disk) and the photometric colors consistent with
an elliptical galaxy. The deVaucouleours profile
Q6: Find galaxies that are blended with a star, output the deblended
galaxy magnitudes.
Q7: Provide a list of star-like objects that are 1% rare.
Q8: Find all objects with unclassified spectra.
Q9: Find quasars with a line width >2000 km/s and
2.5<redshift<2.7.
Q10: Find galaxies with spectra that have an equivalent width in Ha
>40Å (Ha is the main hydrogen spectral line.)
Q11: Find all elliptical galaxies with spectra that have an
anomalous emission line.
Q12: Create a grided count of galaxies with u-g>1 and r<21.5 over
60<declination<70, and 200<right ascension<210, on a grid
of 2’, and create a map of masks over the same grid.
Q13: Create a count of galaxies for each of the HTM triangles
which satisfy a certain color cut, like 0.7u-0.5g-0.2i<1.25 &&
r<21.75, output it in a form adequate for visualization.
Q14: Find stars with multiple measurements and have magnitude
variations >0.1. Scan for stars that have a secondary object
(observed at a different time) and compare their magnitudes.
Q15: Provide a list of moving objects consistent with an asteroid.
Q16: Find all objects similar to the colors of a quasar at
5.5<redshift<6.5.
Q17: Find binary stars where at least one of them has the colors of
a white dwarf.
Q18: Find all objects within 30 arcseconds of one another that have
very similar colors: that is where the color ratios u-g, g-r, r-I
are less than 0.05m.
Q19: Find quasars with a broad absorption line in their spectra and
at least one galaxy within 10 arcseconds. Return both the
quasars and the galaxies.
Q20: For each galaxy in the BCG data set (brightest color galaxy),
in 160<right ascension<170, -25<declination<35 count of
galaxies within 30"of it that have a photoz within 0.05 of that
galaxy.
Also some good queries at:
http://www.sdss.jhu.edu/ScienceArchive/sxqt/sxQT/Example_Queries.html
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Two kinds of SDSS data in an SQL DB
(objects and images all in DB)
• 15M Photo Objects ~ 400 attributes
50K
Spectra
with
~30 lines/
spectrum
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Q15: Fast Moving Objects
• Find near earth asteroids:
SELECT r.objID as rId, g.objId as gId,
dbo.fGetUrlEq(g.ra, g.dec) as url
FROM PhotoObj r, PhotoObj g
WHERE r.run = g.run and r.camcol=g.camcol
and abs(g.field-r.field)<2 -- nearby
-- the red selection criteria
and ((power(r.q_r,2) + power(r.u_r,2)) > 0.111111 )
and r.fiberMag_r between 6 and 22 and r.fiberMag_r < r.fiberMag_g
and r.fiberMag_r < r.fiberMag_i
and r.parentID=0 and r.fiberMag_r < r.fiberMag_u
and r.fiberMag_r < r.fiberMag_z
and r.isoA_r/r.isoB_r > 1.5 and r.isoA_r>2.0
-- the green selection criteria
and ((power(g.q_g,2) + power(g.u_g,2)) > 0.111111 )
and g.fiberMag_g between 6 and 22 and g.fiberMag_g < g.fiberMag_r
and g.fiberMag_g < g.fiberMag_i
and g.fiberMag_g < g.fiberMag_u and g.fiberMag_g < g.fiberMag_z
and g.parentID=0 and g.isoA_g/g.isoB_g > 1.5 and g.isoA_g > 2.0
-- the matchup of the pair
and sqrt(power(r.cx -g.cx,2)+ power(r.cy-g.cy,2)+power(r.cz-g.cz,2))*(10800/PI())< 4.0
and abs(r.fiberMag_r-g.fiberMag_g)< 2.0
• Finds 3 objects in 11 minutes
– (or 52 seconds with an index)
• Ugly,
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but consider the alternatives (c programs an files and…)
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Question &
Answer
Visualization
T
o
o
l
s
Data Visualization
(and human-computer interface)
• Make it easy to ask questions
• Make it easy to understand the answers.
• Bad news: we have had no takers on the
“visualization 20 questions”
• This is still a VERY retro area.
• But. The following demos show some progress.
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Four Talks
• The article we actually wrote
Online Scientific Publication, Curation, Archiving
• The advertised talk
Computer Science Challenges in the VO
• A Web Server (SkyServer) tour
• A Web Service (SdssCutout) tour
• These lead up to Alex Szalay’s talk on Web Services
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SkyServer Tour
http://skyserver.sdss.org/
• Shows benefit of a database
– everything online
– Easy to find things – index helps
– Automatic parallel search is essential
• Beware:
– I’m a lunatic re using databases for everything
– Most people do not put images in DB
– I do, because it is
• Simpler
• Easier to manage
• The right thing to do.
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Four Talks
• The article we actually wrote
Online Scientific Publication, Curation, Archiving
• The advertised talk
Computer Science Challenges in the VO
• A Web Server (SkyServer) tour
• A Web Service (SdssCutout) tour
• Leads up to Alex Szalay’s talk on Web Services
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What’s a Web Service
• Web SERVER:
– Given a url + parameters
– Returns a web page (often dynamic)
You
Web
Server
• Web SERVICE:
– Given a XML document (soap msg)
– Returns an XML document
– Tools make this look like an RPC.
• F(x,y,z) returns (u, v, w)
– Distributed objects for the web.
– + naming, discovery, security,..
• Internet-scale
distributed computing
Your
program
Data
In your
address
space
Web
Service
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Data Federations of Web Services
• Massive datasets live near their owners:
–
–
–
–
Near the instrument’s software pipeline
Near the applications
Near data knowledge and curation
Super Computer centers become Super Data Centers
• Each Archive publishes web services
– Schema: documents the data
– Methods on objects (queries)
• Scientists get “personalized” extracts
• Uniform access to multiple Archives Federation
– A common global schema
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Grid and Web Services Synergy
• I believe the Grid will be many web services
• IETF standards Provide
– Naming
– Authorization / Security / Privacy
– Distributed Objects
Discovery, Definition, Invocation, Object Model
– Higher level services: workflow, transactions, DB,..
• Synergy: commercial Internet & Grid tools
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SDSS Cutout
http://SkyService.pha.jhu.edu/SdssCutout/
• A simple web service
• You can have a copy of the code
• Needs an online database backend
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Four Talks
• The article we actually wrote
Online Scientific Publication, Curation, Archiving
• The advertised talk
Computer Science Challenges in the VO
• A Web Server (SkyServer) tour
• A Web Service (SdssCutout) tour
• Leads up to Alex Szalay’s talk on Web Services
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References and Links
• SkyServer
– http://skyserver.sdss.org/
– http://SkyService.pha.jhu.edu/SdssCutout/
• Virtual Observatory
– http://www.us-vo.org/
– http://www.voforum.org/
• World-Wide Telescope
– paper in Science
V.293 pp. 2037-2038. 14 Sept 2001. (MS-TR-2001-77 word or pdf.)
• SDSS DB:
– Get your personal copy at
http://research.microsoft.com/~gray/sdss
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