a restful web service interface to the atlas cool database
DESCRIPTION
A RESTful Web Service Interface to the ATLAS COOL Database. Shaun Roe. COOL (see talk by A. Valassi , this conference). COOL: A database schema and API designed to be technology neutral (Oracle/ MySQL/SQLite ) Data structure is hierarchical:. - PowerPoint PPT PresentationTRANSCRIPT
A RESTful Web Service... (Shaun Roe, Atlas)
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A RESTful Web Service Interface to the ATLAS
COOL DatabaseShaun Roe
CHEP'09 Prague
A RESTful Web Service... (Shaun Roe, Atlas)
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COOL (see talk by A. Valassi, this conference)
http
://lcg
app.
cern
.ch/
doxy
gen/
COOL
/COO
L_2_
6_0/
doxy
gen/
htm
l/
CHEP'09 Prague
COOL: A database schema and API designed to be technology neutral (Oracle/MySQL/SQLite)
Data structure is hierarchical:Data entry is to a particular folder, channel and with a specific Interval Of Validity (IOV) and tag.=>These form a unique set of coordinates for the datum or resource.Originally in C++, its methods are exposed in Python,
in the ‘PyCool’ module. High Voltage values from the Detector Control System of Atlas SemiConductor Tracker
A RESTful Web Service... (Shaun Roe, Atlas)
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A resource is defined by a unique URLWhat you ‘do’ to that resource is defined by the http method:
POST: Create resource GET: Retrieve resource PUT: Update DELETE: Delete resource
The reply is given via http codes.The format of the answer that you want can be further defined by http headers
REST
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REpresentational StateTransfernoun
verb
e.g. sending a forme.g. A browser normally GETs a web page
‘404 Not Found…’
‘Accept: text/html’ Roy
Field
ing’
s diss
erta
tion:
ht
tp://
www.
ics.u
ci.ed
u/~fi
eldi
ng/p
ubs/
diss
erta
tion/
top.
htm
REST
ful
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Motivation
CHEP'09 Prague A RESTful Web Service... (Shaun Roe, Atlas)
Rewind to 2006…People want data from Cool on the web!Solutions:• Use their own SQL from PHP/Python…• Use a shell script to set up environment, then run the Cool api behind some custom code• Use a cron job to generate local html files..and people want to insert data from the web, too.
A RESTful Web Service... (Shaun Roe, Atlas)
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Aim: Universal Web Service
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Identify resources with url e.g.http://server/database/schema/dbname/some/folder/path/timespan/0-100/channels/23
Use xml as the data transport format.‘GET’ retrieves the values‘POST’ creates the channel in a folder‘PUT’ updates the channel‘DELETE’ deletes the channel from the folderMulti-channel uploads/downloads should be possible. DB Modification should be protected.Additional resources to be matched to a url:Database nodelist, folder description, folder payload definition, list of channels in a folder, list of tags; it should be possible to create and delete databases, folders.
‘Accept: text/xml’
A RESTful Web Service... (Shaun Roe, Atlas)
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Data format: XML
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What aboutJSON ? (see
later)
<channels server="ATLAS_COOLPROD" schema="ATLAS_COOLOFL_DCS" dbname="COMP200" folder="SCT/DCS/CHANSTAT" since="1226271600000000000" until="1226274125000000000" tag="" version="single”><channel id="138950656" since="1226270581000000000" until="1226274125000000000"> <value name="LVCHSTAT_RECV">193</value> <value name="STATE">17</value></channel><channel id="138950656" since="1226274125000000000" until="1226277728000000000"> <value name="LVCHSTAT_RECV">193</value> <value name="STATE">17</value></channel></channels> Definition of an XSD schema allows
validation of data format on upload, or type-ahead and documentation tooltips in an editor: Namespace
s?
(oXygen editor)
XML Schema Description
Java
Scrip
t Obj
ect N
otat
ion
A RESTful Web Service... (Shaun Roe, Atlas)
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Implementation: CherryPy
CHEP'09 Prague
www.cherrypy.orgCherryPy is a Python application server. It is very easy to install and use.The ‘Routes’ module (from Ruby) allows automatic or manual mapping of Python classes and methods to URLs:
d.connect('folder_payload','/:server/:schema/:dbname/*folderPath/payl
oad',controller=restController,action='folderPayload’)
def folderPayload(self, server, schema, dbname, folderPath):
http://myserver.cern.ch/cooldb/ATLAS_COOLPROD/ATLAS_COOL_SCT/DCSP200/SCT/DCS/HV/payload
maps this
to this
The http headers and the methods are also available and can be used to route the URL to the appropriate Python method; other modules for security, caching etc are available.
A RESTful Web Service... (Shaun Roe, Atlas)
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Examples, curl
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Command line examplesCreate a folder:curl 'http://server/DEVDB10/ATLAS_SCT_COMMCOND_DEV/ACALTEST' -u user:pwd -F [email protected] -X POST
Create channels:curl 'http://server/DEVDB10/ATLAS_SCT_COMMCOND_DEV/ACALTEST/test/gain/channels' -u user:pwd -F [email protected] -X POST
Insert values:curl 'http://server/DEVDB10/ATLAS_SCT_COMMCOND_DEV/ACALTEST/test/gain/timespan/0-9223372036854775807/channels’ -u user:pwd -F [email protected] -X PUT
cURL (and libcurl, to use from C, C++, Perl) are standard installations. Other languages have similar libraries: PHP – curl, Java – java.net.url, Python – urllib2 … all are standard installations, so accessing Cool via CherryPy typically does not require any extra setup or libraries.
http
://cu
rl.ha
xx.se
/
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‘In the wild’ examples
CHEP'09 Prague A RESTful Web Service... (Shaun Roe, Atlas)
/** * @author formica */public class CherryPyClient {
private String name = "user.name";private String psswd = "mypass";private String readnodeUrl =
"http://server/ATLAS_SCT_COMMCOND_DEV/ROETEST/Branch/Trial1/payload";private String writenodeUrl =
http://server/ATLAS_SCT_COMMCOND_DEV/ROETEST/Branch/Trial1/timespan/0-100;public String coolGetCherryPy() {
try {URL url = new URL(this.readnodeUrl);java.net.URLConnection conn = url.openConnection();InputStream is = (InputStream) conn.getInputStream();BufferedReader in = new BufferedReader(new InputStreamReader(is));String inputLine = in.readLine();is.close();return inputLine;
} catch (Exception e) {e.printStackTrace();
}return "none";
}
$header=array('Accept: text/xml');//$ch = curl_init();curl_setopt($ch, CURLOPT_HTTPHEADER,$header);curl_setopt($ch, CURLOPT_URL,$url);curl_setopt($ch, CURLOPT_RETURNTRANSFER,1);$format=requested_format();$http_result = curl_exec($ch);if ($format != 'text/xml'){ $dom=domxml_open_mem($http_result);}curl_close($ch);
Java
PHP
httpHeaders={'Accept':'text/xml'}textData=Nonerequest=urllib2.Request(url,textData, httpHeaders)u=urllib2.urlopen(request)xmlDocString = u.read()return xmlDocString
Python
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eXtensible Stylesheet Language for Transformations
Example: Run List
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Search for runs matching criteria, display results;Uses an ‘Ajax’ request to get the CherryPy XML.
Client-side Local server side
XML is inserted directly in the XHTML page, and associated with an XSLT stylesheet to format it as a table
A RESTful Web Service... (Shaun Roe, Atlas)
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Plans, conclusion
CHEP'09 Prague
Use of CherryPy allowed rapid development of a web service interface to Cool which greatly simplified conditions access and adheres to ‘RESTful’ principles.
It was used during 2008 as the engine for the ‘run list’ query page, for various dcs retrieval services, and for insertion of detector status and calibration data; its adoption is growing as a part of web information collations in the detector subsystems.
Future extensions include extra methods for tag viewing, and more flexible output format (e.g. JSON, zipped format…)