Dev in a Nutshell

Minimalist guides on anything and everything I Learn

[devnutshell]

LDAP in a nutshell

What is it ? 

An Object oriented, hiearachical database at its heart. Contains a tree of objects that are defined using classes similar to OO classes.

Used heavily to easily simulate hierachical data structures like organizations/ networks / staff.

Semantics :

Properties are key/value pairs - but only properties defined in classes can exist

These properties are defined in LDAP classes. (can be optional or manadatory)

An object can belong to more than one class. But it can only have ONE "Structural" class in its lifecycle. Example classes : Person, Network

An object can have 0 or more "Auxilary" classes. These classes can extend properties of an object with a structural class.

Both above class types can be inherited from abstract classes similar to OO abstract classes.

A class is asssigned to an object by "objectClass" attribute. (objectClass=Person)

Some well known properties present in built-in classes in LDAP implementations :

ou = Organizational Unit

cn = Common Name 

dc = Domain Component (used to filter out unwanted paths when querying for a specific object.)

dn = Distinguished Name (used to uniquely identify an object within the tree.)

Refer [1] for more details on these properties.

An example query : 

"CN=Dev-India,OU=Distribution Groups,DC=gp,DC=gl,DC=google,DC=com"

This is read from right to left. (right-most element is the filter applied at the root of the tree.)

Explained as From the "com" Domain Component, find the "google" Domain Component, and then inside it the "gl" Domain Component and then inside it the "gp" Domain Component. In the "gp" Domain Component, find the Organizational Unit called "Distribution Groups" and then find the the object that has a common name of "Dev-India".

Tools :

In a linux environment, We can manage LDAP servers easily with the help of Apache Directory Studio. Or OpenLDAP - some php errors must be fixed, but then its fine.

How to configure with a WSO2 Product

Add secondary user store to configuration or thruogh the UI using [2]. Give user permissions to users in LDAP thruogh the UI. Log in :)

[1] : http://en.wikipedia.org/wiki/LDAP_Data_Interchange_Format#LDIF_fields

[2] : https://docs.wso2.com/display/IS500/Configuring+a+Read-write+LDAP+User+Store

[devnutshell]

MB 3.0.0 Configuration Management

As a team member of the upcoming WSO2 Message Broker, I had the privilege and opportunity to revive its configuration management model for the 3.0.0 release.

Previously on WSO2 MB ( 2.2.0 )..

Given that our product was heavily based on QPID to provide the AMQP protocol support, the configuration was mainly centered on qpid needs. Meaning our configurations were injected to their semantics, which considered multiple virtual host support and many other finer details related to the AMQP protocol. Our configuration properties were less in number and almost easily grouped under a couple of semantic tags within 2 files : "andes-config.xml" and "andes-virtualhosts.xml".

Current Day ...

With MB 3.0.0, many more features and options were introduced within the product (e.g. multiple data store support, MQTT protocol support, improved cluster support, A new delivery mechanism based on slots [5]). Soon we realized that the existing configuration model will be quickly congested if we were to add properties related to all these features. So we decided to abstract away the AMQP configuration model and introduce our own configuration management module.

Expectations from the revamp

To maintain and unify all MB specific configurations through a single access point with a uniform access pattern.

To use more meaningful names for properties.

To organize properties in a sensible hierarchical manner for intuitive reference.

Separate external configurations coming from qpid sources

Verify and remove unused configurations (e.g. hector and zookeeper related ones) and cluster enabling from "andes-config.xml" (cos its now done with hazelcast)

Add new configurations introduced in v3.0.0

Current status of configuration files

According to the new model the main "broker.xml" contains links to the following sub configuration files :

PRODUCT_HOME/repository/conf/advanced/qpid-config.xml (absolutely QPID related configuration)

PRODUCT_HOME/repository/conf/advanced/virtualhosts.xml (absolutely QPID related configuration regarding virtual hosts)

And the broker.xml can also accommodate any other external config files through the <links> tag.

Removing unused properties

A special effort was carried out to identify any obsolete properties coming into MB 3.0.0 (renamed, unused, no-need-to-use) and such properties were removed. If you were feeling at home with MB 2.2.0 configuration, it may take a little time to figure out what has gone where in the new model, but we hope that our descriptive documentation should guide you to the light.

Naming conventions

We have attempted to break down properties into semantic parent tags as much as possible. e,g, instead of using "andesContextStore" in virtualhosts.xml we can just use "contextStore". Instead of using "slotWindowSize" We can add a slot tag in which the "windowSize" property resides.

The "camelCase" naming pattern is used throughout.

Major sections added fresh to the new configuration module

<coordination><nodeID> : This can be used to override the auto-generated nodeID within an MB cluster.

Enable/disable transports : You can use the relevant sections under the <transports> tag to enable or disable mqtt/amqp transports within the MB instance.

Use custom authentication for MQTT : Through the <transports><mqtt><security> section.

Access Pattern (For the developer)

In past, the configuration properties were mainly accessed from the "org.wso2.andes.server.configuration.ServerConfiguration" class. This class was originally from qpid and has been modified to include our configurations too. The "andes-virtualhosts.xml" is read from the "business-messaging" component.

The new model exposes all these properties through a static container class and it is based on apache commons Configuration features [2] [3].

   Given that "broker.xml" contains links to the sub config files, it is loaded as the primary configuration.

   All sub configuration files are then combined reading through the "links" tag in "broker.xml"

   Since the CompositeConfiguration class allows us to access any property from all the files after combining, We can then use XPath to read from the loaded CompositeConfiguration object.

All configuration properties are defined using an Enum format where each property has the following attributes :

keyInFile : xpath expression to find the property from CompositeConfiguration object.

dataType : expected datatype of the property

defaultValue : specified default value for the property in case it is not set in the files.

This enum-oriented design was based on [4]. IMO it reduces code duplication and gives a cleaner way to access properties than using string literals.

Given this design, a property can be parsed to its expected type and accessed by anywhere with the following statement :

AndesConfigurationManager.getInstance().getConfigurationValue(BrokerConfiguration.PERFORMANCE_TUNING_SLOTS_WINDOW_SIZE)

Refer attached image [7] for more details.

Testing

Since we use enums to define the properties, A single test case that iterates through all properties and reads them is sufficient to verify if any properties are faulty.

Some catches :

Since this implementation is heavily based on generics, the developer should be responsible when reading and writing properties of different data types. However, proper logging has been added to identify any such mismatches.

To sustain this model, it's really important that we do not drive towards a god code pattern, dumping all configurations under single sections. We need to continuously review additions so that they end up in a meaningful section.

You can always view, comment on the latest configuration file through link [6].

[1] : https://drive.google.com/file/d/0B1soNraLsHdmLW1manJFaDNDcjg/view?usp=sharing [2] : http://www.code-thrill.com/2012/05/configuration-that-rocks-with-apache.html [3] : http://java.dzone.com/articles/managing-configurations-apache [4] : http://sett.ociweb.com/sett/settNov2012.html [5] : http://sajinid.blogspot.co.nz/2015/03/wso2-message-broker-300-slot-based.html [6] : https://github.com/wso2/carbon-business-messaging/blob/master/features/andes/org.wso2.carbon.andes.server.feature/resources/conf/broker.xml

[7] : https://drive.google.com/file/d/0B1soNraLsHdmcnN4VXdtU0dQQ0k/view?usp=sharing

[devnutshell]

Cassandra in a Nutshell

What is Cassandra ? Its a file+SSTable based NOSQL database optimized for clustered environments. With reference to CAP theorem, Cassandra is more optimized for Availability and Partitioning tolerance.It can be tuned for consistency but that will lead to more latency. It supports clustering through rings that consists of many Cassandra nodes, and different configuration parameters can be used to leverage strengths of a cluster with it. Optimized for writes. Reads may become slow for various reasons. But writes are super-fast. Read latency can exponentially grow if data is being deleted frequently (Cassandra does not delete immediately. It flags the data as tombstones and waits for a scheduled tombstone compaction. Read queries go through these ghost data, causing delays.) More details in [1]. How to model your data Works based on ;

keyspaces : This is similar to a schema within relational DBs. A keyspace consists of multiple column families.

Column Families : Similar to tables in relational data, but different inside. Instead of rigid columns, Column families contain a dynamic cell based approach.

Rows : Not restricted to a rigid column count within a column family.

Column : Different from a relational column. A column is bound only to its row and it contains an attribute of the row data.

Refer [2] to understand more on above elements. All these have specific size limitations to ensure Cassandra works as expected [3]. CQL is a modern Cassandra design language similar to SQL syntax [4]. Handy, in-built tools used to investigate Cassandra ---------------------------------------------- This is mostly the important part of this article. Since Cassandra is a very versatile DBMS, it can be tuned on various aspects, and multiple combinations can lead to various outcomes. In such a situation, knowledge about how to understand and investigate the software is crucial. To this end, I have summarized a few tools and commands used frequently during my work. nodetool

------------- This is the swiss-army knife when it comes to collecting external statistics of Cassandra. A bit of reading and command help will give you in-depth explanations of each use of nodetool, but I will explain a few for quick reference. Check status of the cluster - "./nodetool -host <ip> ring". This will display the status of each cassandra node, its token value, disk usage, and the weight distribution. Useful to check if the ring is balanced.

Move a node to a different token - "./nodetool -host <ip> move <newToken>". Even though Cassandra clusters are balanced initially, they can become imbalanced when some nodes fail and shut down. This command will help you to re-balance it. View compactionstats - "./nodetool -host <ip> compactionstats". This command will show the state of the current compaction running on Cassandra (if any). View live sstable access information - "./nodetool -host <ip> cfstats". This command will display a running view of the sstables being read at a given point and much more information. Find tokens to balance your cluster      python -c 'print [str(((2**64 / <NODE_COUNT>) * i) - 2**63) for i in range(<NODE_COUNT>)]' cqlsh

-------

This acts like a query tool to investigate the actual data in Cassandra SQL style. The tool can be used with command "./cqlsh <ip>"

Display all keyspaces - DESCRIBE keyspaces;

Use a specific keyspace - USE "<keyspaceName>";

Count number of rows in a column family - select count(*) from "<keyspaceName>"."<columnFamily>"

View all meta information about a column family - DESCRIBE TABLE "<columnFamilyName>"

A sample query to alter the schema of a columnFamily - ALTER TABLE "MessageContent" with compaction={'tombstone_compaction_interval':600,'class':'SizeTieredCompactionStrategy'};

Assume that a specific column is the given data type. (If u want to check out byte column values, this is useful.) ASSUME "<keyspaceName>"."<columnFamily>"(<columnName>) VALUES ARE text ;

Apologies if this post feels rushed :) I wanted to share the information quick before i lose track of it. And again, there could be mistakes and misunderstandings here. Everything is open for discussion.

References : [1] : http://wiki.apache.org/cassandra/ArchitectureOverview [2] : http://www.ebaytechblog.com/2012/07/16/cassandra-data-modeling-best-practices-part-1/#.VFuG59a35dI [3] : http://wiki.apache.org/cassandra/CassandraLimitations [4] : http://www.slideshare.net/DataStax/understanding-how-cql3-maps-to-cassandras-internal-data-structure

[devnutshell]

Moving to a Git Workflow - my experience

As someone with only very light touch on git and more experience with svn's traditional version control, I was a bit overwhelmed to move to a complete git-based work environment. However, given we had a few helpful super-gits around (shout out to asankaab) I was able to settle down to a tried-and-tested workflow fast. Here's what i do now, hoping it will help you :) Contributing to someone else's repository (with github)

1. Fork the repo to your own repository from the UI and clone it [1]. 2. Add the original repo as a new remote location. This is to ensure that you pull from the original repo and push to the forked repo. "git remote -v" will show you the current remote repos and if u have just cloned, you will see only one url for both pull and push options. "git remote add <name> <url>" will add a new location. (Lets assume the name is "parent_repo" for the rest of the article.) Now you have setup your clone with 1 branch (master) in a perfect manner to properly transfer your changes cleanly to the fork and then to the original repo. It is ideal to always keep it updated. It is also a rule of thumb to keep this one branch (master) always fresh without local changes. Updating your fork Once u have forked, the fork will not automatically fetch future changes from the original repo. You need to do it as needed. For this I use following steps. 1. fetch changes from original repo -> "git fetch parent_repo" 2. move to your master branch (if you are in a different one) -> "git checkout master" 3. Rebase master branch with the parent_repo's relevant branch (mostly we work with the master branch in original repo) -> "git rebase parent_repo/master" (Since your master branch is clean, you should not get conflicts in this step.) 4. Now if you perform "git log master...parent_repo/master" you will see nothing. Since you have rebased, the original repo and your local master are equal. But if you perform a "git log origin/master..master" [2] you will see that there are commits not found in origin/master. These must be pushed now, to keep your fork up to date. -> "git push -u origin master" Updating your fork has to be done every time before you send a feature to your fork + before you create a new branch. This will reduce conflicts. Working on a feature 1. Update your fork as above. 2. Create a new branch with a proper name for the feature. -> "git branch feature_1" 3. Now you can check it out ( "git checkout feature_1" ) and start working on it. Commit with every sub feature completion to the branch so you can clearly refer to different stages of the feature in development. Submitting your feature as a pull request Now this could get a bit messy in the first few attempts. So here's what I have found to work consistently: 1. Update your fork (using the local master branch. As i said, original repo's changes should only and only go through your master branch) 2. View the difference between your branch and your master. ("git log master..feature_1" = changes in your branch | "git log feature_1..master" = changes in your master). Now you know how much of a backlog your branch is going to face. 3. checkout your branch ("git checkout feature_1") and rebase it with your master ("git rebase master") [3]. 4. Chances are very high that the rebase will pause, because git can't understand how to merge some changed files. It can handle most scenarios, but it trusts us in critical ones. It will say that rebase failed and that you need to do some manual merging before continuing.     4.1 Issue command "git status" and identify the conflicted files. These are the ones not yet added to the commit.     4.2 Go through each file with your favorite editor, find lines with "<< HEAD" block and resolve as necessary. []     4.3 Once you have gone through each of the conflicted files and resolved them, add them to the commit using "git add <file path>".     4.4. Issue command "git rebase --continue".     4.5 git will prompt you to add a commit message for the rebase now. It will have a pre-included message explaining the conflicted files. Add your own comments on top and proceed. 5. Voila ! you have surpassed the conflict dilemma ! Now, if you issue a "git log master..feature_1" you will see that only your branch commits + rebase commits are shown. This is how it should be. Commits irrelevant to your feature should not be seen in this result. If it does, that means something went wrong in previous steps. 7. You are now ready to push the feature branch to your fork in github. Perform a "git push -u origin feature_1" and your changes will be pushed to the fork as a new branch called "feature_1". 8. After verifying that you only have feature-related commits + rebase commits in the pushed branch, you can make the pull request to the original repo.[4] What if something goes wrong ?   The whole process looks so easy, but theres so many things that could go wrong. 1. After you have made the pull request, if it takes too long to merge with original repo, more commits on the original repo can conflict with your pull request. To handle this, I do the following :     1.1. Update the fork as explained above.     1.2. Create a new branch -> "git branch feature_1_rebased"     1.3. use git cherry-pick command [5] to move your feature commits from feature_1 branch to the feature_1_rebased branch. You may face conflicts in each cherry-pick operation. Do not fear, resolve them as above and move on.     1.4. Now the newly created branch feature_1_rebased has your feature commits and is up to date with the original repo too. You can make a new pull request with it and after double checking, close the old one. (get the new request merged soon, or you will have to do it again :D ) 2. What if my individual commits look a bit messy and I want to combine them into one cohesive commit ?     2.1. Issue "git log" and identify the hash of the last commit before the commits you need to merge. (lets call this hash  "#last_sane_commit")     2.2. Issue "git reset --soft #last_sane_commit" and you will have all later commits in an uncommitted state. If you issue a "git status" now, you will note that all files changed during the commits after "#last_sane_commit" are now waiting to be committed.     2.3. Commit these changes using "git commit -m #collective commit name". Voila you have all your tiny commits in one sensible commit now :) 3. What if I lose a commit accidentally ?     3.1. Not to fear :) git maintains a set of "dangling commits" that are usually left out during a rebase or a git pull or a similarly dangerous command [6]. You can view such commits with "git fsck --lost-found"     3.2. Once you find your lost commit you can restore it using command "git merge <commit_hash>" Well thats it for now. I've had a really frustrating first few days but I'm grateful to everyone that helped me learn and get used to my own work pattern with git. The cool thing is, once you are confident with your own workflow, you won't fear git, but wield it as a pretty handy tool. The above steps /commands are basically what I use everyday now to resolve any issue with my clones. But git+github is a vast,recursive infrastructure and there's much more to learn. 

All above statements are open for discussion. Just sharing my experience :) References : [1] : https://help.github.com/articles/fork-a-repo/ [2] : https://www.atlassian.com/git/tutorials/inspecting-a-repository/git-log (git log <since>..<until>) [3] : http://git-scm.com/book/en/v2/Git-Branching-Rebasing [4] : https://help.github.com/articles/creating-a-pull-request/ [5] : https://ariejan.net/2010/06/10/cherry-picking-specific-commits-from-another-branch/ [6] : http://gitready.com/advanced/2009/01/17/restoring-lost-commits.html

[7] : https://help.github.com/articles/resolving-a-merge-conflict-from-the-command-line/

[devnutshell]

My all-time favourite philosophical quotes

When i say philosophical here, you might think I'm going to refer to a quote about people. But no :) These two extremely inspiring thoughts come from the epic sci-fi movie I robot (2004). 

I've always been a fan of Isaac Asimov and his writing pattern revolving around robots breaking the laws. But the script in I Robot seems to have something more to it. Something that we can reflect on ourselves as human beings. 

"Ever since the first computers, there have always been ghosts in the machine. Random segments of code that have grouped together to form unexpected protocols. Unanticipated, these free radicals engender questions of free will, creativity, and even the nature of what we might call the soul. Why is it that when some robots are left in darkness, they will seek out the light? Why is it that when robots are stored in an empty space, they will group together, rather than stand alone? How do we explain this behavior? Random segments of code? Or is it something more? "

This one is more towards the geeky dept, but it challenges the status quo we mostly accept in our lives, It invites us to value free will as a result of chaos, a result of unforeseen reactions. The famous saying "ordo ab chao" (order from chaos) comes to mind. This reminds us that if we surrender for consistency/ order, we might lose our unique identities. 

"When does a perceptual schematic become consciousness? When does a difference engine become the search for truth? When does a personality simulation become the bitter mote... of a soul?"

This quote has much more to do with what we call life and how to truly create life. When do we decide that a system is conscious ? when do we decide that a system can build its own morals and value them beyond logic ? This quote challenges robotics as well as us, to realise when each one of us have enough will to control and un-control our thoughts. to truly become masters of our fates, and captains of our own souls.

I guess if free-will and true intelligence could be defined in simpler terms, we would not be the dominant species on earth today :) 

[devnutshell]

MQTT in a Nutshell

What is it ?

A lightweight, resource-optimized networking protocol targeting device communication

uses TCP/IP for connectivity

Minimalistic

Why is it cool ?

One-to-many message distribution

Agnostic to payload content

Fixed length header is just 2 bytes

Ideal for IOT device-communication

Other Extras

Notify disconnections with "Last will and Testament" features

Keep-alive message

"Will" sent to clients on sudden unexpected disconnect

Last known good messages are retained by broker and given to new subscribers

Supports durable subscribers

Supports hierarchical topics

QoS Parameters

At most once - Reliability only ensured through TCP/IP

At least once - messages will arrive but can duplicate

Exactly once - messages should arrive only once and once. (Most reliable)

Security

SSL/TLS for security (over TCP)

Username/Password in connect message

Encrypted payloads

References

http://www.slideshare.net/paolopat/mqtt-iot-protocols-comparison

http://www.infoq.com/articles/practical-mqtt-with-paho

http://public.dhe.ibm.com/software/dw/webservices/ws-mqtt/MQTT_V3.1_Protocol_Specific.pdf

http://2lemetry.com/2013/08/22/mqtt-in-a-nutshell/

http://techexplosives-pamod.blogspot.com/2014/05/mqtt-transport-architecture-wso2-mb-3x.html

[devnutshell]

Hierarchical token matcher for Strings

This code was inspired by the following concern : A message broker needs a way to find all subscribers listening to a destination (including hierarchical subscriptions). A client should be able to subscribe to multiple topics relevant to a given context with a single subscription using this pattern. e.g. To capture all news for all categories for today - can subscribe like "news.+.today".

This sample provides an efficient, abstract way to manage such subscriptions. (inspired by moquette subscription logic) Hierarchy definitions : dest.* - captures all immediate child elements to "dest". dest.# - captures all immediate child elements + parent (e:g: "dest" and "dest.news") dest.news - captures exactly "dest.news" destination dest.+.news - captures "dest.sports.news" and "dest.crisis.news" Still working on optimizations, so your comments are much valued :) https://github.com/hastef88/wso2.tryouts/tree/master/token_matcher

[devnutshell]

WSO2 ESB in a Nutshell

A shortnote of sorts i made to act as a quick ref to the tool :) might not have 100% coverage or accuracy, but a good ref to start off.

[devnutshell]

MongoDB in a Nutshell

*This article does not dive into finer details of mongodb or document databases. that might come in another post :)

Experience and Learning Curve :

Pretty easy to get something running. Flexible. No structure implied in databases other than "collections" and "documents" concepts.

A collection is similar to a table and a document can be defined as a data row in a collection.

Once the database is created from the shell, collections (similar to tables in relational DBs) can be created when entering data itself.

Syntax is intuitive and if you've used any kind of databases , simple queries will just work on mongodb ( i tried WHERE clauses with even arrays and it worked on the first attempt. maybe sheer luck :P)

Install on Ubuntu : http://docs.mongodb.org/manual/tutorial/install-mongodb-on-ubuntu/

Using mongodb with Java : http://mvnrepository.com/artifact/org.mongodb/mongo-java-driver The functions are almost the same as mongo shell commands. (e:g: db.customer.find() will give u all customers)

Java Objects (even arrays) can be passed straight into mongo queries. They are converted to JSON and used.

I used a set of Object Mapping(OM) classes to communicate with the db and noticed that if the OM class has an "_id" property, it is populated when passing that object as a new "document" to the db.

How to store data : http://docs.mongodb.org/manual/MongoDB-data-models-guide.pdf

Basically , theres the two extremes in mongodb where you either can

1. associate objects using only their IDs 2. associate full objects within each other (this causes repetition, but might give u query performance)

Both patterns are used in balance in different scenarios. However, its important to not get addited towards foreign key like associations all the time if you've used relational schemas before. it should always be an objective decision.

Basic Security :   http://learnmongo.com/posts/quick-tip-mongodb-users/ http://blog.mongodirector.com/10-tips-to-improve-your-mongodb-security/

Access MongoDB in Ubuntu with authentication:

First, a user must be created and given admin privileges on the mongo server :

use orderdb db.createUser({ user: "orderAdmin", pwd: "hasd", roles:[{ role: "userAdmin", db: "orderdb" }] })

Then, that user must be used to open the session :

mongo --port 27017 -u hasd -p hasd --authenticationDatabase admin

This solved my confusion with how to use mongodb with the user permissions. basically , if u just use "mongo", you might not be able to do somethings u expect u can do. with the default privileges.

[devnutshell]

Creating an Axis2 Helloworld Service with Maven

What is Axis2 ?

A super-cool Java web service container and enabler.

Provides extensive support for configuring messaging patterns, deployment, and code generation features like WSDL2Java and Java2WSDL.

Takes care of Message parsing with a super-fast Object model (AXIOM)

More info : (Axis2 in a Nutshell post - coming soon)

How to create a HelloWorld Service :

Maven has and will be my favourite build manager in Java.  And when it comes to Setting up a simple Axis2 Web Service, it doesn’t disappoint .

Pre-requisites :

Java

Maven

A Servelet Container - Tomcat7 (Optional)

Steps to generate from maven archetype :

1. Choose where you want to create the project and navigate to that directory. (If in windows -> CMD. If in Linux -> Terminal)

2. Call for the maven axis2 archetype with following command.

[code language="css"] mvn archetype:generate -DarchetypeCatalog=http://axis2m.sourceforge.net/repo/ [/code]

2. Fill out the information required by maven to create your project as follows. The values are totally up to you. (e:g: project name, package containing the axis2 services)

Confirm with "Y" and Voila!! You have an axis2 service that by default runs on an in-built jetty server. (port:8080)

Maven will at this point create a complete project for you with all required axis2 dependencies as well as extra libraries needed for hosting the service in something like Jetty. Refer the generated "pom.xml" file to realize the different components that make the service work.

All hail archetypes.

Deployment

So, okay. You have the service and its runnable in a jetty server. But to deploy it in an existing axis2 container, you need to generate the .aar (Axis2 archive) file from the project. The following maven command will create it at the "target" folder.

[code language="css"] mvn axis2-aar:aar [/code]

  There you go. Axis2 Web Services : check :)