diff --git a/composer.json b/composer.json
index 01efb68..e0cb450 100644
--- a/composer.json
+++ b/composer.json
@@ -12,7 +12,7 @@
   ],
 
   "require": {
-      "svanderburg/pndp": "0.0.1"
+      "svanderburg/pndp": "0.0.2"
   },
   "require-dev": {
       "phpdocumentor/phpdocumentor": "2.9.x"
diff --git a/composer.lock b/composer.lock
index 8390013..1f8cdb3 100644
--- a/composer.lock
+++ b/composer.lock
@@ -4,22 +4,25 @@
         "Read more about it at https://getcomposer.org/doc/01-basic-usage.md#composer-lock-the-lock-file",
         "This file is @generated automatically"
     ],
-    "content-hash": "ca5ed9191c272685068c66b76ed1bae8",
+    "content-hash": "4e19529241df314ff818b5e402ebf060",
     "packages": [
         {
             "name": "svanderburg/pndp",
-            "version": "v0.0.1",
+            "version": "v0.0.2",
             "source": {
                 "type": "git",
                 "url": "https://github.com/svanderburg/pndp.git",
-                "reference": "99b0904e0f2efb35b8f012892912e0d171e9c2da"
+                "reference": "4bfe9c4120c23354ab8dc295957dc3009a39bff0"
             },
             "dist": {
                 "type": "zip",
-                "url": "https://api.github.com/repos/svanderburg/pndp/zipball/99b0904e0f2efb35b8f012892912e0d171e9c2da",
-                "reference": "99b0904e0f2efb35b8f012892912e0d171e9c2da",
+                "url": "https://api.github.com/repos/svanderburg/pndp/zipball/4bfe9c4120c23354ab8dc295957dc3009a39bff0",
+                "reference": "4bfe9c4120c23354ab8dc295957dc3009a39bff0",
                 "shasum": ""
             },
+            "require-dev": {
+                "phpdocumentor/phpdocumentor": "2.9.x"
+            },
             "bin": [
                 "bin/pndp-build"
             ],
@@ -41,7 +44,7 @@
                 }
             ],
             "description": "PNDP: An internal DSL for Nix in PHP",
-            "time": "2017-09-11T21:11:09+00:00"
+            "time": "2017-10-22T12:43:22+00:00"
         }
     ],
     "packages-dev": [
@@ -1499,16 +1502,16 @@
         },
         {
             "name": "symfony/config",
-            "version": "v2.8.27",
+            "version": "v2.8.28",
             "source": {
                 "type": "git",
                 "url": "https://github.com/symfony/config.git",
-                "reference": "0b8541d18507d10204a08384640ff6df3c739ebe"
+                "reference": "1dbeaa8e2db4b29159265867efff075ad961558c"
             },
             "dist": {
                 "type": "zip",
-                "url": "https://api.github.com/repos/symfony/config/zipball/0b8541d18507d10204a08384640ff6df3c739ebe",
-                "reference": "0b8541d18507d10204a08384640ff6df3c739ebe",
+                "url": "https://api.github.com/repos/symfony/config/zipball/1dbeaa8e2db4b29159265867efff075ad961558c",
+                "reference": "1dbeaa8e2db4b29159265867efff075ad961558c",
                 "shasum": ""
             },
             "require": {
@@ -1551,20 +1554,20 @@
             ],
             "description": "Symfony Config Component",
             "homepage": "https://symfony.com",
-            "time": "2017-04-12T14:07:15+00:00"
+            "time": "2017-10-04T18:56:36+00:00"
         },
         {
             "name": "symfony/console",
-            "version": "v2.8.27",
+            "version": "v2.8.28",
             "source": {
                 "type": "git",
                 "url": "https://github.com/symfony/console.git",
-                "reference": "c0807a2ca978e64d8945d373a9221a5c35d1a253"
+                "reference": "f81549d2c5fdee8d711c9ab3c7e7362353ea5853"
             },
             "dist": {
                 "type": "zip",
-                "url": "https://api.github.com/repos/symfony/console/zipball/c0807a2ca978e64d8945d373a9221a5c35d1a253",
-                "reference": "c0807a2ca978e64d8945d373a9221a5c35d1a253",
+                "url": "https://api.github.com/repos/symfony/console/zipball/f81549d2c5fdee8d711c9ab3c7e7362353ea5853",
+                "reference": "f81549d2c5fdee8d711c9ab3c7e7362353ea5853",
                 "shasum": ""
             },
             "require": {
@@ -1612,7 +1615,7 @@
             ],
             "description": "Symfony Console Component",
             "homepage": "https://symfony.com",
-            "time": "2017-08-27T14:29:03+00:00"
+            "time": "2017-10-01T21:00:16+00:00"
         },
         {
             "name": "symfony/debug",
@@ -1673,16 +1676,16 @@
         },
         {
             "name": "symfony/event-dispatcher",
-            "version": "v2.8.27",
+            "version": "v2.8.28",
             "source": {
                 "type": "git",
                 "url": "https://github.com/symfony/event-dispatcher.git",
-                "reference": "1377400fd641d7d1935981546aaef780ecd5bf6d"
+                "reference": "7fe089232554357efb8d4af65ce209fc6e5a2186"
             },
             "dist": {
                 "type": "zip",
-                "url": "https://api.github.com/repos/symfony/event-dispatcher/zipball/1377400fd641d7d1935981546aaef780ecd5bf6d",
-                "reference": "1377400fd641d7d1935981546aaef780ecd5bf6d",
+                "url": "https://api.github.com/repos/symfony/event-dispatcher/zipball/7fe089232554357efb8d4af65ce209fc6e5a2186",
+                "reference": "7fe089232554357efb8d4af65ce209fc6e5a2186",
                 "shasum": ""
             },
             "require": {
@@ -1729,7 +1732,7 @@
             ],
             "description": "Symfony EventDispatcher Component",
             "homepage": "https://symfony.com",
-            "time": "2017-06-02T07:47:27+00:00"
+            "time": "2017-10-01T21:00:16+00:00"
         },
         {
             "name": "symfony/filesystem",
@@ -1782,16 +1785,16 @@
         },
         {
             "name": "symfony/finder",
-            "version": "v2.8.27",
+            "version": "v2.8.28",
             "source": {
                 "type": "git",
                 "url": "https://github.com/symfony/finder.git",
-                "reference": "4f4e84811004e065a3bb5ceeb1d9aa592630f9ad"
+                "reference": "a945724b201f74d543e356f6059c930bb8d10c92"
             },
             "dist": {
                 "type": "zip",
-                "url": "https://api.github.com/repos/symfony/finder/zipball/4f4e84811004e065a3bb5ceeb1d9aa592630f9ad",
-                "reference": "4f4e84811004e065a3bb5ceeb1d9aa592630f9ad",
+                "url": "https://api.github.com/repos/symfony/finder/zipball/a945724b201f74d543e356f6059c930bb8d10c92",
+                "reference": "a945724b201f74d543e356f6059c930bb8d10c92",
                 "shasum": ""
             },
             "require": {
@@ -1827,20 +1830,20 @@
             ],
             "description": "Symfony Finder Component",
             "homepage": "https://symfony.com",
-            "time": "2017-06-01T20:52:29+00:00"
+            "time": "2017-10-01T21:00:16+00:00"
         },
         {
             "name": "symfony/polyfill-mbstring",
-            "version": "v1.5.0",
+            "version": "v1.6.0",
             "source": {
                 "type": "git",
                 "url": "https://github.com/symfony/polyfill-mbstring.git",
-                "reference": "7c8fae0ac1d216eb54349e6a8baa57d515fe8803"
+                "reference": "2ec8b39c38cb16674bbf3fea2b6ce5bf117e1296"
             },
             "dist": {
                 "type": "zip",
-                "url": "https://api.github.com/repos/symfony/polyfill-mbstring/zipball/7c8fae0ac1d216eb54349e6a8baa57d515fe8803",
-                "reference": "7c8fae0ac1d216eb54349e6a8baa57d515fe8803",
+                "url": "https://api.github.com/repos/symfony/polyfill-mbstring/zipball/2ec8b39c38cb16674bbf3fea2b6ce5bf117e1296",
+                "reference": "2ec8b39c38cb16674bbf3fea2b6ce5bf117e1296",
                 "shasum": ""
             },
             "require": {
@@ -1852,7 +1855,7 @@
             "type": "library",
             "extra": {
                 "branch-alias": {
-                    "dev-master": "1.5-dev"
+                    "dev-master": "1.6-dev"
                 }
             },
             "autoload": {
@@ -1886,20 +1889,20 @@
                 "portable",
                 "shim"
             ],
-            "time": "2017-06-14T15:44:48+00:00"
+            "time": "2017-10-11T12:05:26+00:00"
         },
         {
             "name": "symfony/process",
-            "version": "v2.8.27",
+            "version": "v2.8.28",
             "source": {
                 "type": "git",
                 "url": "https://github.com/symfony/process.git",
-                "reference": "57e52a0a6a80ea0aec4fc1b785a7920a95cb88a8"
+                "reference": "26c9fb02bf06bd6b90f661a5bd17e510810d0176"
             },
             "dist": {
                 "type": "zip",
-                "url": "https://api.github.com/repos/symfony/process/zipball/57e52a0a6a80ea0aec4fc1b785a7920a95cb88a8",
-                "reference": "57e52a0a6a80ea0aec4fc1b785a7920a95cb88a8",
+                "url": "https://api.github.com/repos/symfony/process/zipball/26c9fb02bf06bd6b90f661a5bd17e510810d0176",
+                "reference": "26c9fb02bf06bd6b90f661a5bd17e510810d0176",
                 "shasum": ""
             },
             "require": {
@@ -1935,20 +1938,20 @@
             ],
             "description": "Symfony Process Component",
             "homepage": "https://symfony.com",
-            "time": "2017-07-03T08:04:30+00:00"
+            "time": "2017-10-01T21:00:16+00:00"
         },
         {
             "name": "symfony/stopwatch",
-            "version": "v2.8.27",
+            "version": "v2.8.28",
             "source": {
                 "type": "git",
                 "url": "https://github.com/symfony/stopwatch.git",
-                "reference": "e02577b841394a78306d7b547701bb7bb705bad5"
+                "reference": "28ee62ea4736431ca817cdaebcb005663e9cd1cb"
             },
             "dist": {
                 "type": "zip",
-                "url": "https://api.github.com/repos/symfony/stopwatch/zipball/e02577b841394a78306d7b547701bb7bb705bad5",
-                "reference": "e02577b841394a78306d7b547701bb7bb705bad5",
+                "url": "https://api.github.com/repos/symfony/stopwatch/zipball/28ee62ea4736431ca817cdaebcb005663e9cd1cb",
+                "reference": "28ee62ea4736431ca817cdaebcb005663e9cd1cb",
                 "shasum": ""
             },
             "require": {
@@ -1984,7 +1987,7 @@
             ],
             "description": "Symfony Stopwatch Component",
             "homepage": "https://symfony.com",
-            "time": "2017-04-12T14:07:15+00:00"
+            "time": "2017-10-01T21:00:16+00:00"
         },
         {
             "name": "symfony/translation",
@@ -2052,16 +2055,16 @@
         },
         {
             "name": "symfony/validator",
-            "version": "v2.8.27",
+            "version": "v2.8.28",
             "source": {
                 "type": "git",
                 "url": "https://github.com/symfony/validator.git",
-                "reference": "864ba6865e253a7ffc3db5629af676cfdc3bd104"
+                "reference": "1531ddfd96efd1b2c231cbf45f22e652a8f67925"
             },
             "dist": {
                 "type": "zip",
-                "url": "https://api.github.com/repos/symfony/validator/zipball/864ba6865e253a7ffc3db5629af676cfdc3bd104",
-                "reference": "864ba6865e253a7ffc3db5629af676cfdc3bd104",
+                "url": "https://api.github.com/repos/symfony/validator/zipball/1531ddfd96efd1b2c231cbf45f22e652a8f67925",
+                "reference": "1531ddfd96efd1b2c231cbf45f22e652a8f67925",
                 "shasum": ""
             },
             "require": {
@@ -2121,7 +2124,7 @@
             ],
             "description": "Symfony Validator Component",
             "homepage": "https://symfony.com",
-            "time": "2017-08-27T14:29:03+00:00"
+            "time": "2017-10-01T21:00:16+00:00"
         },
         {
             "name": "twig/twig",
diff --git a/src/Composer2Nix/Dependencies/HgDependency.php b/src/Composer2Nix/Dependencies/HgDependency.php
deleted file mode 100644
index 52a0d09..0000000
--- a/src/Composer2Nix/Dependencies/HgDependency.php
+++ /dev/null
@@ -1,47 +0,0 @@
-<?php
-namespace Composer2Nix\Dependencies;
-use PNDP\NixGenerator;
-use PNDP\AST\NixExpression;
-use PNDP\AST\NixFunInvocation;
-
-/**
- * Represents a Mercurial dependency.
- */
-class HgDependency extends Dependency
-{
-	/**
-	 * Constructs a new Mercurial dependency instance.
-	 *
-	 * @param array $package An array of package configuration properties
-	 * @param array $sourceObj An array of download properties
-	 */
-	public function __construct(array $package, array $sourceObj)
-	{
-		parent::__construct($package, $sourceObj);
-	}
-
-	/**
-	 * @see NixAST::toNixAST
-	 */
-	public function toNixAST()
-	{
-		$dependency = parent::toNixAST();
-
-		$hash = shell_exec('nix-prefetch-hg "'.$this->sourceObj['url'].'" '.$this->sourceObj["reference"]);
-
-		if($hash === false)
-			throw new Exception("Error while invoking nix-prefetch-hg");
-		else
-		{
-			$dependency["src"] = new NixFunInvocation(new NixExpression("fetchhg"), array(
-				"name" => strtr($this->package["name"], "/", "-").'-'.$this->sourceObj["reference"],
-				"url" => $this->sourceObj["url"],
-				"rev" => $this->sourceObj["reference"],
-				"sha256" => $hash
-			));
-		}
-
-		return $dependency;
-	}
-}
-?>
diff --git a/src/Composer2Nix/Dependencies/SVNDependency.php b/src/Composer2Nix/Dependencies/SVNDependency.php
deleted file mode 100644
index ad479d6..0000000
--- a/src/Composer2Nix/Dependencies/SVNDependency.php
+++ /dev/null
@@ -1,47 +0,0 @@
-<?php
-namespace Composer2Nix\Dependencies;
-use PNDP\NixGenerator;
-use PNDP\AST\NixExpression;
-use PNDP\AST\NixFunInvocation;
-
-/**
- * Represents a Subversion dependency.
- */
-class SVNDependency extends Dependency
-{
-	/**
-	 * Constructs a new Subversion dependency instance.
-	 *
-	 * @param array $package An array of package configuration properties
-	 * @param array $sourceObj An array of download properties
-	 */
-	public function __construct(array $package, array $sourceObj)
-	{
-		parent::__construct($package, $sourceObj);
-	}
-
-	/**
-	 * @see NixAST::toNixAST
-	 */
-	public function toNixAST()
-	{
-		$dependency = parent::toNixAST();
-
-		$hash = shell_exec('nix-prefetch-svn "'.$this->sourceObj['url'].'" '.$this->sourceObj["reference"]);
-
-		if($hash === false)
-			throw new Exception("Error while invoking nix-prefetch-svn");
-		else
-		{
-			$dependency["src"] = new NixFunInvocation(new NixExpression("fetchsvn"), array(
-				"name" => strtr($this->package["name"], "/", "-").'-'.$this->sourceObj["reference"],
-				"url" => $this->sourceObj["url"],
-				"rev" => $this->sourceObj["reference"],
-				"sha256" => $hash
-			));
-		}
-
-		return $dependency;
-	}
-}
-?>
diff --git a/src/Composer2Nix/Expressions/CompositionExpression.php b/src/Composer2Nix/Expressions/CompositionExpression.php
index a9a3a1f..8f4e97f 100644
--- a/src/Composer2Nix/Expressions/CompositionExpression.php
+++ b/src/Composer2Nix/Expressions/CompositionExpression.php
@@ -2,6 +2,7 @@
 namespace Composer2Nix\Expressions;
 use PNDP\NixGenerator;
 use PNDP\AST\NixAttrReference;
+use PNDP\AST\NixASTNode;
 use PNDP\AST\NixExpression;
 use PNDP\AST\NixFunction;
 use PNDP\AST\NixFunInvocation;
@@ -10,7 +11,6 @@ use PNDP\AST\NixImport;
 use PNDP\AST\NixInherit;
 use PNDP\AST\NixLet;
 use PNDP\AST\NixObject;
-use Composer2Nix\NixASTNode;
 
 /**
  * A representation of a composition expression whose purpose is to compose
@@ -52,7 +52,7 @@ class CompositionExpression extends NixASTNode
 	}
 
 	/**
-	 * @see NixAST::toNixAST
+	 * @see NixAST::toNixAST()
 	 */
 	public function toNixAST()
 	{
diff --git a/src/Composer2Nix/Expressions/PackagesExpression.php b/src/Composer2Nix/Expressions/PackagesExpression.php
index d6de421..805e155 100644
--- a/src/Composer2Nix/Expressions/PackagesExpression.php
+++ b/src/Composer2Nix/Expressions/PackagesExpression.php
@@ -1,9 +1,10 @@
 <?php
 namespace Composer2Nix\Expressions;
 use Composer2Nix\ComposerConfig;
-use Composer2Nix\Dependencies\Dependency;
+use Composer2Nix\Sources\Source;
 use PNDP\NixGenerator;
 use PNDP\AST\NixAttrSet;
+use PNDP\AST\NixASTNode;
 use PNDP\AST\NixExpression;
 use PNDP\AST\NixFile;
 use PNDP\AST\NixFunction;
@@ -13,7 +14,6 @@ use PNDP\AST\NixLet;
 use PNDP\AST\NixNoDefault;
 use PNDP\AST\NixObject;
 use PNDP\AST\NixURL;
-use Composer2Nix\NixASTNode;
 
 /**
  * A representation of a packages expression specifying all dependencies
@@ -51,15 +51,16 @@ class PackagesExpression extends NixASTNode
 
 	private function generateDependenciesExpr(array $packages)
 	{
-		$dependencies = array();
+		$sources = array();
 
 		foreach($packages as $package)
 		{
-			$dependency = Dependency::constructDependency($package, $this->preferredInstall);
-			$dependencies[$package["name"]] = $dependency;
+			$source = Source::constructSource($package, $this->preferredInstall);
+			$source->fetch();
+			$sources[$package["name"]] = $source;
 		}
 
-		return new NixAttrSet($dependencies);
+		return new NixAttrSet($sources);
 	}
 
 	private function generatePackageMetaDataExpr()
@@ -101,7 +102,7 @@ class PackagesExpression extends NixASTNode
 	}
 
 	/**
-	 * @see NixAST::toNixAST
+	 * @see NixAST::toNixAST()
 	 */
 	public function toNixAST()
 	{
diff --git a/src/Composer2Nix/NixASTNode.php b/src/Composer2Nix/NixASTNode.php
deleted file mode 100644
index f20023a..0000000
--- a/src/Composer2Nix/NixASTNode.php
+++ /dev/null
@@ -1,30 +0,0 @@
-<?php
-// TODO: move to PNDP
-
-namespace Composer2Nix;
-use PNDP\NixGenerator;
-use PNDP\AST\NixObject;
-
-/**
- * A representation of a Nix expression that is non-terminal, i.e. it is
- * composed out of other objects.
- */
-abstract class NixASTNode extends NixObject
-{
-	/**
-	 * Returns a compound object that will be converted into a Nix
-	 * expression.
-	 *
-	 * @return mixed A composition of objects that can be converted into a Nix expression
-	 */
-	abstract public function toNixAST();
-
-	/**
-	 * @see NixObject::toNixExpr
-	 */
-	public function toNixExpr($indentLevel, $format)
-	{
-		return NixGenerator::phpToIndentedNix($this->toNixAST(), $indentLevel, $format);
-	}
-}
-?>
diff --git a/src/Composer2Nix/Dependencies/GitDependency.php b/src/Composer2Nix/Sources/GitSource.php
similarity index 58%
rename from src/Composer2Nix/Dependencies/GitDependency.php
rename to src/Composer2Nix/Sources/GitSource.php
index 81a5ab5..8ab7597 100644
--- a/src/Composer2Nix/Dependencies/GitDependency.php
+++ b/src/Composer2Nix/Sources/GitSource.php
@@ -1,5 +1,5 @@
 <?php
-namespace Composer2Nix\Dependencies;
+namespace Composer2Nix\Sources;
 use PNDP\NixGenerator;
 use PNDP\AST\NixExpression;
 use PNDP\AST\NixFunInvocation;
@@ -7,8 +7,10 @@ use PNDP\AST\NixFunInvocation;
 /**
  * Represents a Git dependency.
  */
-class GitDependency extends Dependency
+class GitSource extends Source
 {
+	public $url;
+
 	/**
 	 * Constructs a new Git dependency instance.
 	 *
@@ -21,12 +23,10 @@ class GitDependency extends Dependency
 	}
 
 	/**
-	 * @see NixAST::toNixAST
+	 * @see Source::fetch()
 	 */
-	public function toNixAST()
+	public function fetch()
 	{
-		$dependency = parent::toNixAST();
-
 		$outputStr = shell_exec('nix-prefetch-git "'.$this->sourceObj['url'].'" '.$this->sourceObj["reference"]);
 
 		if($outputStr === false)
@@ -34,17 +34,25 @@ class GitDependency extends Dependency
 		else
 		{
 			$output = json_decode($outputStr, true);
-			$hash = $output["sha256"];
-
-			$dependency["src"] = new NixFunInvocation(new NixExpression("fetchgit"), array(
-				"name" => strtr($this->package["name"], "/", "-").'-'.$this->sourceObj["reference"],
-				"url" => $this->sourceObj["url"],
-				"rev" => $this->sourceObj["reference"],
-				"sha256" => $hash
-			));
+			$this->hash = $output["sha256"];
 		}
+	}
 
-		return $dependency;
+	/**
+	 * @see NixAST::toNixAST()
+	 */
+	public function toNixAST()
+	{
+		$ast = parent::toNixAST();
+
+		$ast["src"] = new NixFunInvocation(new NixExpression("fetchgit"), array(
+			"name" => strtr($this->package["name"], "/", "-").'-'.$this->sourceObj["reference"],
+			"url" => $this->sourceObj["url"],
+			"rev" => $this->sourceObj["reference"],
+			"sha256" => $this->hash
+		));
+
+		return $ast;
 	}
 }
 ?>
diff --git a/src/Composer2Nix/Sources/HgSource.php b/src/Composer2Nix/Sources/HgSource.php
new file mode 100644
index 0000000..92a1def
--- /dev/null
+++ b/src/Composer2Nix/Sources/HgSource.php
@@ -0,0 +1,53 @@
+<?php
+namespace Composer2Nix\Sources;
+use PNDP\NixGenerator;
+use PNDP\AST\NixExpression;
+use PNDP\AST\NixFunInvocation;
+
+/**
+ * Represents a Mercurial source.
+ */
+class HgSource extends Source
+{
+	public $hash;
+
+	/**
+	 * Constructs a new Mercurial dependency instance.
+	 *
+	 * @param array $package An array of package configuration properties
+	 * @param array $sourceObj An array of download properties
+	 */
+	public function __construct(array $package, array $sourceObj)
+	{
+		parent::__construct($package, $sourceObj);
+	}
+
+	/**
+	 * @see Source::fetch()
+	 */
+	public function fetch()
+	{
+		$this->hash = shell_exec('nix-prefetch-hg "'.$this->sourceObj['url'].'" '.$this->sourceObj["reference"]);
+
+		if($this->hash === false)
+			throw new Exception("Error while invoking nix-prefetch-hg");
+	}
+
+	/**
+	 * @see NixAST::toNixAST()
+	 */
+	public function toNixAST()
+	{
+		$ast = parent::toNixAST();
+
+		$ast["src"] = new NixFunInvocation(new NixExpression("fetchhg"), array(
+			"name" => strtr($this->package["name"], "/", "-").'-'.$this->sourceObj["reference"],
+			"url" => $this->sourceObj["url"],
+			"rev" => $this->sourceObj["reference"],
+			"sha256" => $this->hash
+		));
+
+		return $ast;
+	}
+}
+?>
diff --git a/src/Composer2Nix/Dependencies/PathDependency.php b/src/Composer2Nix/Sources/PathSource.php
similarity index 53%
rename from src/Composer2Nix/Dependencies/PathDependency.php
rename to src/Composer2Nix/Sources/PathSource.php
index 8a79a8d..905df72 100644
--- a/src/Composer2Nix/Dependencies/PathDependency.php
+++ b/src/Composer2Nix/Sources/PathSource.php
@@ -1,13 +1,15 @@
 <?php
-namespace Composer2Nix\Dependencies;
+namespace Composer2Nix\Sources;
 use PNDP\NixGenerator;
 use PNDP\AST\NixFile;
 
 /**
- * Represents a dependency to a local filesystem path.
+ * Represents a source referring to a local filesystem path.
  */
-class PathDependency extends Dependency
+class PathSource extends Source
 {
+	public $path;
+
 	/**
 	 * Constructs a new Git dependency instance.
 	 *
@@ -20,13 +22,21 @@ class PathDependency extends Dependency
 	}
 
 	/**
-	 * @see NixAST::toNixAST
+	 * @see Source::fetch()
+	 */
+	public function fetch()
+	{
+		$this->path = $this->sourceObj['url'];
+	}
+
+	/**
+	 * @see NixAST::toNixAST()
 	 */
 	public function toNixAST()
 	{
-		$dependency = parent::toNixAST();
-		$dependency["src"] = new NixFile($this->sourceObj['url']);
-		return $dependency;
+		$ast = parent::toNixAST();
+		$ast["src"] = new NixFile($this->path);
+		return $ast;
 	}
 }
 ?>
diff --git a/src/Composer2Nix/Sources/SVNSource.php b/src/Composer2Nix/Sources/SVNSource.php
new file mode 100644
index 0000000..6864235
--- /dev/null
+++ b/src/Composer2Nix/Sources/SVNSource.php
@@ -0,0 +1,51 @@
+<?php
+namespace Composer2Nix\Sources;
+use PNDP\NixGenerator;
+use PNDP\AST\NixExpression;
+use PNDP\AST\NixFunInvocation;
+
+/**
+ * Represents a Subversion source.
+ */
+class SVNSource extends Source
+{
+	/**
+	 * Constructs a new Subversion dependency instance.
+	 *
+	 * @param array $package An array of package configuration properties
+	 * @param array $sourceObj An array of download properties
+	 */
+	public function __construct(array $package, array $sourceObj)
+	{
+		parent::__construct($package, $sourceObj);
+	}
+
+	/**
+	 * @see Source::fetch()
+	 */
+	public function fetch()
+	{
+		$this->hash = shell_exec('nix-prefetch-svn "'.$this->sourceObj['url'].'" '.$this->sourceObj["reference"]);
+
+		if($this->hash === false)
+			throw new Exception("Error while invoking nix-prefetch-svn");
+	}
+
+	/**
+	 * @see NixAST::toNixAST()
+	 */
+	public function toNixAST()
+	{
+		$ast = parent::toNixAST();
+
+		$ast["src"] = new NixFunInvocation(new NixExpression("fetchsvn"), array(
+			"name" => strtr($this->package["name"], "/", "-").'-'.$this->sourceObj["reference"],
+			"url" => $this->sourceObj["url"],
+			"rev" => $this->sourceObj["reference"],
+			"sha256" => $this->hash
+		));
+
+		return $ast;
+	}
+}
+?>
diff --git a/src/Composer2Nix/Dependencies/Dependency.php b/src/Composer2Nix/Sources/Source.php
similarity index 64%
rename from src/Composer2Nix/Dependencies/Dependency.php
rename to src/Composer2Nix/Sources/Source.php
index be70f80..3e6eab9 100644
--- a/src/Composer2Nix/Dependencies/Dependency.php
+++ b/src/Composer2Nix/Sources/Source.php
@@ -1,25 +1,25 @@
 <?php
-namespace Composer2Nix\Dependencies;
-use Composer2Nix\NixASTNode;
+namespace Composer2Nix\Sources;
+use PNDP\AST\NixASTNode;
 use Exception;
 
 /**
  * Represents a dependency of a composer package that can be converted into a
  * Nix expression that obtains it.
  */
-abstract class Dependency extends NixASTNode
+abstract class Source extends NixASTNode
 {
 	public $package;
 
 	protected $sourceObj;
 
 	/**
-	 * Creates a new dependency instance.
+	 * Creates a new source instance.
 	 *
 	 * @param array $package An array of package configuration properties
 	 * @param array $sourceObj An array of download properties
 	 */
-	protected function __construct(array $package, array $sourceObj)
+	public function __construct(array $package, array $sourceObj)
 	{
 		$this->package = $package;
 		$this->sourceObj = $sourceObj;
@@ -48,47 +48,52 @@ abstract class Dependency extends NixASTNode
 	}
 
 	/**
-	 * Constructs a new dependency from a package configuration.
+	 * Constructs a new source from a package configuration.
 	 *
 	 * @param array $package An array of package configuration properties
 	 * @param string $preferredInstall Preferred installation type (source or dist)
-	 * @return A specific kind of dependency object derived from the dependencies' type
+	 * @return A specific kind of dependency object derived from the source's type
 	 * @throw An exception if the type is unrecognized
 	 */
-	public static function constructDependency(array $package, $preferredInstall)
+	public static function constructSource(array $package, $preferredInstall)
 	{
-		$sourceObj = Dependency::selectSourceObject($preferredInstall, $package);
+		$sourceObj = Source::selectSourceObject($preferredInstall, $package);
 
 		switch($sourceObj["type"])
 		{
 			case "path":
-				return new PathDependency($package, $sourceObj);
+				return new PathSource($package, $sourceObj);
 			case "zip":
-				return new ZipDependency($package, $sourceObj);
+				return new ZipSource($package, $sourceObj);
 			case "git":
-				return new GitDependency($package, $sourceObj);
+				return new GitSource($package, $sourceObj);
 			case "hg":
-				return new HgDependency($package, $sourceObj);
+				return new HgSource($package, $sourceObj);
 			case "svn":
-				return new SVNDependency($package, $sourceObj);
+				return new SVNSource($package, $sourceObj);
 			default:
 				throw new Exception("Cannot convert dependency of type: ".$sourceObj["type"]);
 		}
 	}
 
 	/**
-	 * @see NixAST::toNixAST
+	 * Fetches the package metadata from the external source.
+	 */
+	abstract public function fetch();
+
+	/**
+	 * @see NixAST::toNixAST()
 	 */
 	public function toNixAST()
 	{
-		$dependency = array();
+		$ast = array();
 
 		if(array_key_exists("target-dir", $this->package))
-			$dependency["targetDir"] = $this->package["target-dir"];
+			$ast["targetDir"] = $this->package["target-dir"];
 		else
-			$dependency["targetDir"] = "";
+			$ast["targetDir"] = "";
 
-		return $dependency;
+		return $ast;
 	}
 }
 ?>
diff --git a/src/Composer2Nix/Dependencies/ZipDependency.php b/src/Composer2Nix/Sources/ZipSource.php
similarity index 58%
rename from src/Composer2Nix/Dependencies/ZipDependency.php
rename to src/Composer2Nix/Sources/ZipSource.php
index 23c6871..5062370 100644
--- a/src/Composer2Nix/Dependencies/ZipDependency.php
+++ b/src/Composer2Nix/Sources/ZipSource.php
@@ -1,5 +1,5 @@
 <?php
-namespace Composer2Nix\Dependencies;
+namespace Composer2Nix\Sources;
 use PNDP\NixGenerator;
 use PNDP\AST\NixExpression;
 use PNDP\AST\NixFile;
@@ -7,10 +7,12 @@ use PNDP\AST\NixFunInvocation;
 use PNDP\AST\NixURL;
 
 /**
- * Represents a Zip package dependency.
+ * Represents a Zip package source.
  */
-class ZipDependency extends Dependency
+class ZipSource extends Source
 {
+	public $hash;
+
 	/**
 	 * Constructs a new Zip dependency instance.
 	 *
@@ -23,12 +25,10 @@ class ZipDependency extends Dependency
 	}
 
 	/**
-	 * @see NixAST::toNixAST
+	 * @see Source::fetch()
 	 */
-	public function toNixAST()
+	public function fetch()
 	{
-		$dependency = parent::toNixAST();
-
 		if($this->sourceObj["reference"] == "")
 			$reference = "";
 		else
@@ -36,27 +36,38 @@ class ZipDependency extends Dependency
 
 		if(substr($this->sourceObj["url"], 0, 7) === "http://" || substr($this->sourceObj["url"], 0, 8) === "https://")
 		{
-			$hash = shell_exec('nix-prefetch-url "'.$this->sourceObj['url'].'"');
+			$this->hash = shell_exec('nix-prefetch-url "'.$this->sourceObj['url'].'"');
 
-			if($hash === null)
+			if($this->hash === false)
 				throw new Exception("Error while invoking nix-prefetch-url");
-			else
-			{
-				$src = new NixFunInvocation(new NixFile("fetchurl"), array(
-					"url" => new NixURL($this->sourceObj["url"]),
-					"sha256" => substr($hash, 0, -1)
-				));
-			}
 		}
 		else
-			$src = new NixFile($this->sourceObj['url']);
+			$this->hash = null;
+	}
 
-		$dependency["src"] = new NixFunInvocation(new NixExpression("composerEnv.buildZipPackage"), array(
+	/**
+	 * @see NixAST::toNixAST()
+	 */
+	public function toNixAST()
+	{
+		$ast = parent::toNixAST();
+
+		if($this->hash === null)
+			$src = new NixFile($this->sourceObj['url']);
+		else
+		{
+			$src = new NixFunInvocation(new NixFile("fetchurl"), array(
+				"url" => new NixURL($this->sourceObj["url"]),
+				"sha256" => substr($this->hash, 0, -1)
+			));
+		}
+
+		$ast["src"] = new NixFunInvocation(new NixExpression("composerEnv.buildZipPackage"), array(
 			"name" => strtr($this->package["name"], "/", "-").$reference,
 			"src" => $src
 		));
 
-		return $dependency;
+		return $ast;
 	}
 }
 ?>