diff --git a/src/alire-properties-versions.ads b/src/alire-properties-versions.ads
new file mode 100644
index 00000000..70e3d1f9
--- /dev/null
+++ b/src/alire-properties-versions.ads
@@ -0,0 +1,9 @@
+with Semantic_Versioning;
+
+package Alire.Properties.Versions is
+
+   type Version is new Property with record
+      Value : Semantic_Versioning.Version;
+   end record;
+
+end Alire.Properties.Versions;
diff --git a/src/alire-properties.ads b/src/alire-properties.ads
index 083eff5a..541bfb3e 100644
--- a/src/alire-properties.ads
+++ b/src/alire-properties.ads
@@ -1,33 +1,18 @@
-private with Ada.Containers.Indefinite_Holders;
+with Ada.Containers.Indefinite_Vectors;
 
 package Alire.Properties with Preelaborate is
 
    --  Properties are the general mechanism used to store all info about a release.
    --  They can be specialized (e.g. in version, platform, compiler) but that can be transparent to the user.
 
+   --  Since a property can be checked against a variety of conditions, this would require fully fledged
+   --  multiple inheritance for the simplest design.
+   --  Instead, a first check of matching tags is done and then the checks can proceed.
+
    type Property is tagged null record;
 
+   package Property_Vectors is new Ada.Containers.Indefinite_Vectors (Positive, Property'Class);
 
-
-   type Checker is tagged private;
-   --  A checker verifies against some internally stored data that a property is satisfied.
-   --  Here we provide the basic storage of values but the actual checking function must be overridden
-   --    for particular checks.
-
-   function New_Check (Using : Property'Class) return Checker'Class;
-
-   function Value (Check : Checker'Class) return Property'Class;
-
-   function Check (This : Checker'Class; Prop : Property'Class) return Boolean;
-   --  This classwide helper will match the stored property tag against the one given.
-   --  If the match the actual checking function is used, otherwise False is returned
-
-private
-
-   package Property_Holders is new Ada.Containers.Indefinite_Holders (Property'Class);
-
-   type Checker is tagged record
-      Property : Property_Holders.Holder;
-   end record;
+   subtype Vector is Property_Vectors.Vector;
 
 end Alire.Properties;
diff --git a/src/alire-requisites.ads b/src/alire-requisites.ads
new file mode 100644
index 00000000..01cd0e96
--- /dev/null
+++ b/src/alire-requisites.ads
@@ -0,0 +1,47 @@
+with Ada.Containers.Indefinite_Multiway_Trees;
+
+with Alire.Properties;
+
+package Alire.Requisites with Preelaborate is
+
+   use Properties;
+
+   type Requisite is tagged null record;
+   --  A Requisite verifies against some internally stored data that a property is satisfied.
+   --  Here we provide the basic storage of values but the actual checking function must be overridden
+   --    for particular checks.
+
+   function Is_Applicable (R : Requisite; P : Property'Class) return Boolean is (False);
+   --  Initially there is no compatibility. See helper package below
+
+   package Requisite_Trees is new Ada.Containers.Indefinite_Multiway_Trees (Requisite'Class);
+
+   subtype Tree is Requisite_Trees.Tree;
+
+   --  The following package is the building block to be used to define new compatibility checks.
+   --  Here we tie a class of properties and requisites (e.g., versions and version sets) that make sense.
+   --  A release has a list of properties, and a tree of requisites to be applied to potential dependencies.
+
+   generic
+      type Compatible_Property is new Property with private;
+   package Property_Checker is
+
+      type Requisite is new Requisites.Requisite with null record;
+
+      function Is_Satisfied (R : Requisite; P : Compatible_Property) return Boolean;
+      --  This is the important function to override by Requisite implementations
+
+      --  The remainder methods are utilities that do not require modifications by the client.
+
+      overriding function Is_Applicable (R : Requisite; P : Property'Class) return Boolean is
+        (P in Compatible_Property);
+      --  Convenience for the evaluator to determine which properties might satisfy a requisite
+
+      function Cast (R : Requisite; P : Property'Class) return Compatible_Property'Class is
+        (Compatible_Property'Class (P))
+      with Pre => R.Is_Applicable (P);
+      --  Convenience cast that can be done inside the package, but not outside, so it must be available here!
+
+   end Property_Checker;
+
+end Alire.Requisites;