What is data serialization?

Question

First of all, I couldn't get clear definition of it from WikiPedia or even from serialize function in the PHP manual. I need to know some cases where we need the term serialization and how things are going without it? In other words, Where you need serialization and without it your code will be missing some important feature.

Answer 1

What is serialization?

Serialization encodes objects into another format.
For example you have an array in PHP like this:

$array = array("a" => 1, "b" => 2, "c" => array("a" => 1, "b" => 2));

And then you want to store it in file or send to other application.

There are several format choices, but the idea is the same: The array has to be encoded (or you could say "translated"), into text or bytes, that can be written to a file or sent via the network.
For example, in PHP, if you:

$data = serialize($array);

you will get this:

a:3:{s:1:"a";i:1;s:1:"b";i:2;s:1:"c";a:2:{s:1:"a";i:1;s:1:"b";i:2;}}

This is PHP's particular serializing format that PHP understands, and it works vice versa, so you are able to use it to deserialize objects.
For example, you stored a serialized array in a file, and you want it back in your code as an array:

$array = unserialize($data);

But you could choose a different serialization format, for example, JSON:

$json = json_encode($array);

will give you this:

{"a":1,"b":2,"c":{"a":1,"b":2}}

The result is not only easily saved, read by human eye, or sent via network, but is also understandable by almost every other language (JavaScript, Java, C#, C++, ...)

Conclusion
Serialization translate objects to another format, in case you want to store or share data.

Are there any situations, where you cannot do anything, but serialize it?

No. But serialization usually makes things easier.

Are JSON and PHP format the only possible formats?
No, no, no and one more time no. There are plenty of formats.

• XML (e.g. using a schema like WSDL or XHTML)
• Bytes, Protobuf, etc.
• Yaml
• ...
• ...
• Your own formats (you can create your own format for serialization and use it, but that is a big thing to do and is not worth it, most of the time)

Answer 2

Serialization is the process of converting some in-memory object to another format that could be used to either store in a file or sent over the network. Deserialization is the inverse process meaning the actual object instance is restored from the given serialized representation of the object. This is very useful when communicating between various systems.

The serialization format could be either interoperable or non-interoperable. Interoperable formats (such as JSON, XML, ...) allow for serializing some object using a given platform and deserializing it using a different platform. For example with JSON you could use javascript to serialize the object and send it over the network to a PHP script that will deserialize the object and use it.

The serialize() PHP function uses an non-interoperable format. This means that only PHP could be used to both serialize and deserialize the object back.

You could use the json_encode and json_decode() functions in order to serialize/deserialize PHP objects using the JSON interoperable format.

Answer 3

Serialization is the process of turning data (e.g. variables) into a representation such as a string, that can easily be written and read back from for example a file or the database.

Use cases? There are many, but generally it revolves around the idea of taking a complex, nested array or object and turning it into a simple string that can be saved and read later to retrieve the same structure. For example, provided you have in php:

$blub = array();
$blub['a'] = 1;
$blub['a']['b'] = 4;
$blub['b'] = 27;
$blub['b']['b'] = 46;

Instead of going through every array member individually and writing it one could just:

$dataString = serialize($blub);

And the serialized array is ready to be written anywhere as a simple string, in such a way that retrieving this string again and doing unserialize() over it gets you the exact same array structure you had before. Yes, it's really that simple.

Answer 4

I need to know some cases we need the term serialization and how things are going without it?

Serialization can become handy if you need to store complete structures (like an invoice with all associated data like customer address, sender address, product positions, tax caclulcations etc) that are only valid at a certain point in time.

All these data will change in the future, new tax regulations might come, the address of a customer changes, products go out of life. But still the invoice needs to be valid and stored.

This is possible with serialization. Like a snapshot. The object in memory are serialized into a (often like in PHP) binary form that can be just stored. It can be brought back to live later on (and in a different context). Like with this invoice example: In ten years, the data can still be read and the invoice object is the same as it was ten years earlier.

In other word, Where you must need serialization and without it your code will be missing some important feature.

That was one example. It's not that you always needs that, but if things become more complex, serialization can be helpful.

Answer 5

Since you've tagged it with javascript, one kind of serialization could be form serialization.

Here are the references for the jQuery and prototype.JS equivalents.

What they basically do is serialize form input values into comma-separated name-value pairs.

So considering an actual usage..

$.ajax({
   url : 'insert.php?a=10,b=15' //values serialized via .serialize()
   type: 'GET'
});

And you would probably do $GET["a"] to retrieve those values, I'm not familiar with PHP though.