“qebu: an advanced metadata editor”, paolo pasini polytechnic university of turin

“QEbu: an advanced metadata editor” Paolo Pasini Polytechnic University of Turin Get in contact: [email protected]

#FIATIFTADubai2013 Paolo Pasini: “QEbu- an advanced metadata editor”

Copyright © of this presenta1on is the property of the author(s). FIAT/IFTA is granted permission to reproduce copies of this work for purposes relevant to the above conference and future communica1on by FIAT/IFTA without limita1on, provided that the author(s), source and copyright no1ce are included in each copy. For other uses, including extended quota1on, please contact the author(s).

Contents

}  Introduction }  Model design }  XML management }  GUI ◦  Interface ◦  Data management

}  Conclusion

#FIATIFTADubai2013 Paolo Pasini: QEbu – an advanced metadata editor

EBU Core Metadata Set

}  Has been developed by the EBU Expert Community on Metadata (ECM).

}  Latest revised in october 2011 (version 1.3).

}  It makes use of Simple Dublin Core metadata elements as well as more complex structures with deeper expressivity and flexibility.

}  The general aim is to define a minimum list of attributes characterising a media resource.


QEbu: Project specifica1ons

}  QEbu provides an editor for metadata following the EBU Core Metadata Set.

}  The user is able to produce new metadata documents or edit existing ones.

}  A simple graphic interface helps the user in his work by providing: ◦  Instant validation on all input fields; ◦  Dictionaries for dictionary based attributes; ◦  In-place documentation for all metadata

elements.


Why a GUI?

}  Editing XML by hand is a hard task, especially with high complex structure definition.

}  Using a GUI, the user can focus on metadata content, instead of worry about the format in which metadata will be stored.


Contents


}  Conclusion


From XML to C++

}  “A class for each element” }  Yes, but with as much code reuse as

possible.

}  Exploiting objects composition and inheritance, we tried to keep the number of defined classes to a reasonable minimum.


Managing IDRefs

}  RightsType and PublicationType elements contain a reference to a FormatType ◦  It’s a strong relation enforced by the usage of

ID-IDREF(s) types in the schema definition.

}  Corresponding classes have been designed to contain a pointer to the format. ◦  Why not a simple string with the ID?

}  However pointers require careful handling: ◦  What happens if a format is deleted?


Root Format Map

}  We have introduced a root format map in the top-level metadata element: ◦  Key: format ID; ◦  Value: formatType pointer and a list of listeners.

}  A listener is an object which needs to know if a format is deleted (i.e. rightsType and publicationType).


Contents


}  Conclusion


The issue

}  Provide manipulation functionalities over the contents of an XML file of interest, and allow creation of a valid document from scratch.

}  It is required a way to map model objects from, and to, XML documents, in a sensible and coherent way


Which way?

}  The requirements of the application, and the complexity of the schema, pretty much call for DOM loud and clear.

}  DOM makes for an easier management of the contents, and cover all the requirements needed.

}  What about performance?


Valida1on

}  A fundamental aspect of working with XML is the validation of the contents… ◦  …but Qt doesn’t provide anything robust

enough. }  In this case it is better to delegate to

something else, which does just that: ◦  xmllint, from libxml2

}  What if an input file does not validate? }  Validation comes for free when working

from scratch.


XML to memory…

}  This step is performed by EbuParser, which visits recursively the document model managing one node at a time.

}  “A class for each element, and for each class its parser”.

}  We defined a pattern to achieve code homogeneity and readability.


EbuParser snippet


T* EbuParser::parseT(const QDomElement &element)

{

// Sanity check for node element validity

if (element.isNull()) {

m_errorMsg = “T element is null";

return 0;

}

// Create custom object T

T *obj = new T;

// Get attribute(s).

t attributeName = element.attribute("attributeName");

// Sanity check for attribute validity, according to

// the specific type

if (!attributeName.isValid())

obj->setAttributeName(attributeName);

// all the attributes parsed...

// Get element(s)

// A node list is expected in this example

QDomNodeList nodeList =

element.elementsByTagName("tagName");

for (int i=0; i < nodeList.size(); ++i) {

QDomElement el = nodeList.item(i).toElement();

// In case of nested elements with a given name, which

// are not dicrect children of the current node, skip

if (el.parentNode() != element)

continue;

// Recursively parse the child element, like we just

// did with its parent

ChildT *child = parseChildT(el);

// In case the returned child is not valid (i.e. null)

if (!child) {

// Destroy the parent as well and return failure

delete obj;

return 0;

}

// In case of success append the child in the proper

// structure

obj->tagName().append(child);

}

// Proceed with more children elements…

return obj;

}

…and back!

}  The steps from memory to XML are performed by EbuSerializer, which is the dual counterpart of our custom parser just described.

}  Once again, to iterate is human, to recurse divine.


EbuSerializer snippet


QDomElement EbuSerializer::serializeT(T *obj)

{

// Create an empty unnamed element

QDomElement l = m_doc.createElement(" ");

// Serialize attribute(s), performing sanity check

// prior to write data

if (!obj->attribute1().isValid())

l.setAttribute("attribute1", obj->attribute1());

if (!obj->attribute2().isValid())

l.setAttribute("attribute2", obj->attribute2());

// ...all the attributes

if (!obj->element1().isEmpty()) {

// Create inner empty unnamed element

// This is just a text node

QDomElement e = m_doc.createElement(" ");

e.setTagName("innerElementName");

QDomText textNode =

m_doc.createTextNode(l->element1());

e.appendChild(textNode);

l.appendChild(e);

}

if (obj->element2()) {

// This is a child element node

QDomElement e = serializeT2(obj->element2());

e.setTagName("anotherInnerElementName");

l.appendChild(e);

}

// For all the elements...

return l;

}


Infinite descent

}  The EBU Core metadata allows the definition of element types that may include content of the very same type.

}  The recursive approach has proven to be the only way worth implementing to handle with ease the schema specifics.

Contents


}  Conclusion



User interface

}  For almost every object in the model, a dedicated form has been created.

}  As a rule of thumb, the principle criteria followed can be summarized like: ◦  Whenever possible attributes are managed via edit

fields; ◦  In case of range-restricted values, pickers are

employed; ◦  Children elements come with their own form, but few

exceptions (i.e. groups); ◦  If possible attributes/elements are grouped together

in a meaningful way; ◦  Recycle as much as possible exploiting composition.


Stack of Forms

}  The user interface employs a custom pattern based on stackable forms.

}  The users can see only one form at a time }  No popup dialogs }  Linear path of navigation


Lists, lists everywhere…

}  Many elements include subelements with cardinality [0..*].

}  This poses some problems in the UI design: ◦  How to avoid congesting the interface? ◦  How to deal with the coexistence of lists and [0..1]

elements?


Users first aid

}  QEbu offers several features intended for this goal: ◦  A quickstart tutorial; ◦  A navigation bar; ◦  Embedded documentation ◦  Auto completion

Contents


}  Conclusion



Data input

}  Design challenges: ◦  Provide user-friendly forms; ◦  Propose values from dictionaries; ◦  Grant an instantaneous input validation.

}  Qt framework already provides many widgets for different type of input.

}  But something was still missing…


Some examples


Auto-‐comple1on

}  Some fields are meant to store a reference to standard lists of contents.

}  The reference scheme are listed in EBU Core documentation.

}  Those values are retrieved from a set of XML files downloaded from EBU website, when available.


Schema-‐related problems

}  EBU Core schema uses XML Schema types. }  It does not restrict them enough. }  What is the use of:

•  duplicated timezones? •  years, months, days of duration? •  negative durations?

}  It permits to express values which can be meaningless or discordant.

}  This may cause troubles for any program which wants to handle those metadata.

Contents


}  Conclusion



Tes1ng

}  It is known that testing should be done by someone not involved in the coding phase… ◦  … but sometimes it is everything you got.

}  Being realistic, it is more a matter of where bugs lie, rather than whether bugs are there.


Future works

}  Internationalization (i18n) ◦  The code is already ready for i18n since all text

strings have been surrounded by Qt special macros.

}  Forms re-design ◦  We treated each field and attribute equally. ◦  Feedback from EBU-EMC experts who actually

use such metadata could lead to better tailored forms with relevant contents more easily accessible.

}  Dynamic download of attribute dictionaries from EBU website.


QEbu is free so\ware

}  QEbu is released under terms of the GNU General Public License 3 as published by the Free Software Foundation.

}  The application is built using Qt 4.8 framework by Nokia. ◦  http://qt.nokia.com/products/library

}  XML validation requires libxml2 to be installed.


QEbu project in numbers

}  7 weeks }  5 people }  252 commits }  39428 LOC ◦  8438 in model/* ◦  5485 in fileproc/* ◦  25505 in ui/*

}  149 classes ◦  68 in model/* ◦  3 in fileproc/* ◦  78 in ui/*

“QEbu: an advanced metadata editor” Paolo Pasini Polytechnic University of Turin Get in contact: [email protected]


Copyright © of this presenta1on is the property of the author(s). FIAT/IFTA is granted permission to reproduce copies of this work for purposes relevant to the above conference and future communica1on by FIAT/IFTA without limita1on, provided that the author(s), source and copyright no1ce are included in each copy. For other uses, including extended quota1on, please contact the author(s).

“qebu: an advanced metadata editor”, paolo pasini polytechnic university of turin

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