diff --git a/wfassoc/src/lib.rs b/wfassoc/src/lib.rs
index f457771..986714c 100644
--- a/wfassoc/src/lib.rs
+++ b/wfassoc/src/lib.rs
@@ -5,98 +5,212 @@
 compile_error!("Crate wfassoc is only supported on Windows.");
 
 pub mod utilities;
-pub mod concept;
+pub mod win32;
 
-// pub mod utilities;
-// pub mod winconcept;
-// pub mod win32ext;
-// pub mod winregext;
+use std::fmt::Display;
+use std::str::FromStr;
+use thiserror::Error as TeError;
+use winreg::RegKey;
 
-// use std::collections::HashMap;
-// use thiserror::Error as TeError;
+// region: Error Process
 
-// /// Error occurs in this module.
-// #[derive(Debug, TeError)]
-// pub enum Error {}
+/// Error occurs in this module.
+#[derive(Debug, TeError)]
+pub enum Error {
+    #[error("can not perform this operation because lack essential privilege.")]
+    NoPrivilege,
+    #[error("{0}")]
+    BadRegOp(#[from] std::io::Error),
+    #[error("{0}")]
+    UnexpectedBlankKey(#[from] win32::regext::BlankPathError),
+}
 
-// /// Result type used in this module.
-// type Result<T> = std::result::Result<T, Error>;
+// endregion
 
-// /// Schema is the sketchpad of complete Program.
-// ///
-// /// We will create a Schema first, fill some properties, add file extensions,
-// /// then convert it into immutable Program for following using.
-// #[derive(Debug)]
-// pub struct Schema {
-//     identifier: String,
-//     path: String,
-//     clsid: String,
-//     icons: HashMap<String, String>,
-//     behaviors: HashMap<String, String>,
-//     exts: HashMap<String, SchemaExt>,
-// }
+// region: Scope and View
 
-// /// Internal used struct as the Schema file extensions hashmap value type.
-// #[derive(Debug)]
-// struct SchemaExt {
-//     name: String,
-//     icon: String,
-//     behavior: String,
-// }
+/// The scope where wfassoc will register and unregister.
+#[derive(Debug, Copy, Clone)]
+pub enum Scope {
+    /// Scope for current user.
+    User,
+    /// Scope for all users under this computer.
+    System,
+}
 
-// impl Schema {
-//     pub fn new() -> Self {
-//         Self {
-//             identifier: String::new(),
-//             path: String::new(),
-//             clsid: String::new(),
-//             icons: HashMap::new(),
-//             behaviors: HashMap::new(),
-//             exts: HashMap::new(),
-//         }
-//     }
+/// The view when wfassoc querying infomations.
+#[derive(Debug, Copy, Clone)]
+pub enum View {
+    /// The view of current user.
+    User,
+    /// The view of system.
+    System,
+    /// Hybrid view of User and System.
+    /// It can be seen as that we use System first and then use User to override any existing items.
+    Hybrid,
+}
 
-//     pub fn set_identifier(&mut self, identifier: &str) -> Result<()> {}
+/// The error occurs when cast View into Scope.
+#[derive(Debug, TeError)]
+#[error("hybrid view can not be cast into any scope")]
+pub struct TryFromViewError {}
 
-//     pub fn set_path(&mut self, exe_path: &str) -> Result<()> {}
+impl TryFromViewError {
+    fn new() -> Self {
+        Self {}
+    }
+}
 
-//     pub fn set_clsid(&mut self, clsid: &str) -> Result<()> {}
+impl From<Scope> for View {
+    fn from(value: Scope) -> Self {
+        match value {
+            Scope::User => Self::User,
+            Scope::System => Self::System,
+        }
+    }
+}
 
-//     pub fn add_icon(&mut self, name: &str, value: &str) -> Result<()> {}
+impl TryFrom<View> for Scope {
+    type Error = TryFromViewError;
 
-//     pub fn add_behavior(&mut self, name: &str, value: &str) -> Result<()> {}
+    fn try_from(value: View) -> Result<Self, Self::Error> {
+        match value {
+            View::User => Ok(Self::User),
+            View::System => Ok(Self::System),
+            View::Hybrid => Err(TryFromViewError::new()),
+        }
+    }
+}
 
-//     pub fn add_ext(
-//         &mut self,
-//         ext: &str,
-//         ext_name: &str,
-//         ext_icon: &str,
-//         ext_behavior: &str,
-//     ) -> Result<()> {
-//     }
+impl Scope {
+    /// Check whether we have enough privilege when operating in current scope.
+    /// If we have, simply return, otherwise return error.
+    fn check_privilege(&self) -> Result<(), Error> {
+        if matches!(self, Self::System if !win32::utilities::has_privilege()) {
+            Err(Error::NoPrivilege)
+        } else {
+            Ok(())
+        }
+    }
+}
 
-//     pub fn into_program(self) -> Result<Program> {
-//         Program::new(self)
-//     }
-// }
+// endregion
 
-// /// Program is a complete and immutable program representer
-// pub struct Program {}
+#[derive(Debug, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
+pub struct AppPathsKey {
+    key: win32::concept::FileName,
+}
 
-// impl TryFrom<Schema> for Program {
-//     type Error = Error;
+#[derive(Debug, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
+pub struct ApplicationsKey {
+    key: win32::concept::FileName,
+}
 
-//     fn try_from(value: Schema) -> std::result::Result<Self, Self::Error> {
-//         Self::new(value)
-//     }
-// }
+// region: File Extension Key
 
-// impl Program {
-//     pub fn new(schema: Schema) -> Result<Self> {}
-// }
+#[derive(Debug, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
+pub struct ExtKey {
+    ext: win32::concept::Ext,
+}
+
+impl ExtKey {
+    fn open_scope(&self, scope: Scope) -> Result<Option<RegKey>, Error> {
+        use winreg::enums::{HKEY_CURRENT_USER, HKEY_LOCAL_MACHINE, KEY_READ, KEY_WRITE};
+
+        // check privilege
+        scope.check_privilege()?;
+        // get the root key
+        let hk = match scope {
+            Scope::User => RegKey::predef(HKEY_CURRENT_USER),
+            Scope::System => RegKey::predef(HKEY_LOCAL_MACHINE),
+        };
+        // navigate to classes
+        let classes = hk.open_subkey_with_flags("Software\\Classes", KEY_READ | KEY_WRITE)?;
+        // open extension key if possible
+        let thisext = win32::regext::try_open_subkey_with_flags(
+            &classes,
+            win32::regext::blank_path_guard(self.ext.dotted_inner())?,
+            KEY_READ | KEY_WRITE,
+        )?;
+        // okey
+        Ok(thisext)
+    }
+
+    fn open_view(&self, view: View) -> Result<Option<RegKey>, Error> {
+        use winreg::enums::{HKEY_CLASSES_ROOT, HKEY_CURRENT_USER, HKEY_LOCAL_MACHINE, KEY_READ};
+
+        // navigate to extension container
+        let hk = match view {
+            View::User => RegKey::predef(HKEY_CURRENT_USER),
+            View::System => RegKey::predef(HKEY_LOCAL_MACHINE),
+            View::Hybrid => RegKey::predef(HKEY_CLASSES_ROOT),
+        };
+        let classes = match view {
+            View::User | View::System => {
+                hk.open_subkey_with_flags("Software\\Classes", KEY_READ)?
+            }
+            View::Hybrid => hk.open_subkey_with_flags("", KEY_READ)?,
+        };
+        // open extension key if possible
+        let thisext = win32::regext::try_open_subkey_with_flags(
+            &classes,
+            win32::regext::blank_path_guard(self.ext.dotted_inner())?,
+            KEY_READ,
+        )?;
+        // okey
+        Ok(thisext)
+    }
 
 
-// #[derive(Debug, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
-// pub struct ExtKey {
-//     inner: winconcept::Ext
-// }
+}
+
+// endregion
+
+// region: ProgId Key
+
+// region: Losse ProgId
+
+/// The enum representing a losse Programmatic Identifiers (ProgId).
+///
+/// In real world, not all software developers are willing to following Microsoft suggestions to use ProgId,
+/// They use string which do not have any regulation as ProgId.
+/// This enum is designed for handling this scenario.
+#[derive(Debug, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
+enum LosseProgId {
+    Plain(String),
+    Strict(win32::concept::ProgId),
+}
+
+impl Display for LosseProgId {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self {
+            LosseProgId::Plain(v) => write!(f, "{}", v),
+            LosseProgId::Strict(v) => write!(f, "{}", v),
+        }
+    }
+}
+
+impl From<&str> for LosseProgId {
+    fn from(s: &str) -> Self {
+        // match it for standard ProgId first
+        if let Ok(v) = win32::concept::ProgId::from_str(s) {
+            Self::Strict(v)
+        } else {
+            // fallback with other
+            Self::Plain(s.to_string())
+        }
+    }
+}
+
+// endregion
+
+// region: ProgId Key
+
+#[derive(Debug, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
+pub struct ProgIdKey {
+    progid: LosseProgId,
+}
+
+// endregion
+
+// endregion
diff --git a/wfassoc/src/utilities.rs b/wfassoc/src/utilities.rs
index 4ee9816..e5c7c06 100644
--- a/wfassoc/src/utilities.rs
+++ b/wfassoc/src/utilities.rs
@@ -23,7 +23,7 @@ macro_rules! debug_println {
     };
 }
 
-// region OS String Related
+// region: OS String Related
 
 /// The error occurs when casting `OsStr` into `str`.
 #[derive(Debug, TeError)]
diff --git a/wfassoc/src/win32.rs b/wfassoc/src/win32.rs
new file mode 100644
index 0000000..2788102
--- /dev/null
+++ b/wfassoc/src/win32.rs
@@ -0,0 +1,3 @@
+pub mod concept;
+pub mod utilities;
+pub mod regext;
\ No newline at end of file
diff --git a/wfassoc/src/concept.rs b/wfassoc/src/win32/concept.rs
similarity index 91%
rename from wfassoc/src/concept.rs
rename to wfassoc/src/win32/concept.rs
index 4e51471..62d48b5 100644
--- a/wfassoc/src/concept.rs
+++ b/wfassoc/src/win32/concept.rs
@@ -59,6 +59,12 @@ impl Ext {
     pub fn inner(&self) -> &str {
         &self.body
     }
+
+    /// Get the body part of file extension (with leading dot)
+    pub fn dotted_inner(&self) -> String {
+        // Reuse Display trait result
+        self.to_string()
+    }
 }
 
 /// The error occurs when try parsing string into FileExt.
@@ -123,7 +129,7 @@ impl BadProgIdPartError {
 /// `[Vendor or Application].[Component].[Version]` format.
 ///
 /// Additionally, `[Version]` part is optional.
-/// 
+///
 /// However, most of applications do no follow this standard,
 /// this scenario is not convered by this struct in there.
 /// It should be done by other structs in other places.
@@ -237,7 +243,7 @@ impl FromStr for ProgId {
 
 /// The struct representing Windows CLSID looks like
 /// `{26EE0668-A00A-44D7-9371-BEB064C98683}` (case insensitive).
-/// 
+///
 /// Please note that the curly brace is the essential part of CLSID.
 #[derive(Debug, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
 pub struct Clsid {
@@ -312,7 +318,7 @@ impl ParseIconRefStrError {
 
 /// The struct representing an Icon Reference String
 /// looks like `%SystemRoot%\System32\imageres.dll,-72`.
-/// 
+///
 /// As far as I know, the minus token `-` does nothing in this string.
 /// The following number is just the index.
 pub struct IconRefStr {
@@ -405,7 +411,7 @@ impl ParseStrRefStrError {
 
 /// The struct representing an String Reference String
 /// looks like `@%SystemRoot%\System32\shell32.dll,-30596`.
-/// 
+///
 /// As far as I know, the minus token `-` does nothing in this string.
 /// The following number is just the index.
 pub struct StrRefStr {
@@ -757,3 +763,67 @@ impl FromStr for ExpandString {
 }
 
 // endregion
+
+// region: File Name
+
+pub type BadFileNameError = ParseFileNameError;
+
+/// The struct representing a legal Windows file name.
+#[derive(Debug, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
+pub struct FileName {
+    /// The validated legal Windows file name.
+    filename: String,
+}
+
+impl FileName {
+    /// Create a new file name.
+    /// 
+    /// `filename` is the file name for validating.
+    /// This function will validate whether given file name is legal in Windows,
+    /// in other words, checking whether it contain illegal words or Windows reserved name in given name 
+    /// such as `?`, `COM` and etc.
+    pub fn new(filename: &str) -> Result<Self, BadFileNameError> {
+        Self::from_str(filename)
+    }
+
+    /// Get the validated file name.
+    pub fn inner(&self) -> &str {
+        &self.filename
+    }
+}
+
+/// The error occurs when constructing FileName with bad file name.
+#[derive(Debug, TeError)]
+#[error("given file name is illegal in Windows")]
+pub enum ParseFileNameError {
+    /// Given string has embedded NUL.
+    EmbeddedNul(#[from] widestring::error::ContainsNul<WideChar>),
+    /// Given string has illegal char as Windows file name.
+    InvalidChar,
+}
+
+impl Display for FileName {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        self.filename.fmt(f)
+    }
+}
+
+impl FromStr for FileName {
+    type Err = ParseFileNameError;
+    
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
+        use windows_sys::Win32::UI::Shell::PathCleanupSpec;
+
+        // Make buffer and call function.
+        let mut spec = WideCString::from_str(s)?;
+        let rv = unsafe { PathCleanupSpec(std::ptr::null(), spec.as_mut_ptr()) };
+        if rv != 0 {
+            return Err(ParseFileNameError::InvalidChar);
+        }
+
+        // Build self and return
+        Ok(Self { filename: s.to_string() })
+    }
+}
+
+// endregion
diff --git a/wfassoc/src/winregext.rs b/wfassoc/src/win32/regext.rs
similarity index 98%
rename from wfassoc/src/winregext.rs
rename to wfassoc/src/win32/regext.rs
index 49a8773..647c7e9 100644
--- a/wfassoc/src/winregext.rs
+++ b/wfassoc/src/win32/regext.rs
@@ -14,7 +14,7 @@ use winreg::types::FromRegValue;
 /// Get the subkey with given name.
 ///
 /// If error occurs when fetching given subkey, it return `Err(...)`,
-/// otherwise, it will return `Ok(Some(...))` if aubkey is existing,
+/// otherwise, it will return `Ok(Some(...))` if subkey is existing,
 /// or `Ok(None)` if there is no suchsub key.
 ///
 /// Comparing with the function provided by winreg,
diff --git a/wfassoc/src/win32ext.rs b/wfassoc/src/win32/utilities.rs
similarity index 100%
rename from wfassoc/src/win32ext.rs
rename to wfassoc/src/win32/utilities.rs
diff --git a/wfassoc/tests/concept.rs b/wfassoc/tests/concept.rs
index 8fad225..526f0c4 100644
--- a/wfassoc/tests/concept.rs
+++ b/wfassoc/tests/concept.rs
@@ -1,5 +1,5 @@
 use std::str::FromStr;
-use wfassoc::concept::*;
+use wfassoc::win32::concept::*;
 
 // region: File Extension
 
@@ -230,3 +230,25 @@ fn test_expand_string() {
 }
 
 // endregion
+
+// region: File Name
+
+#[test]
+fn test_file_name() {
+    fn ok_tester(s: &str) {
+        let rv = FileName::from_str(s);
+        assert!(rv.is_ok());
+        let rv = rv.unwrap();
+        assert_eq!(s, rv.inner());
+    }
+    fn err_tester(s: &str) {
+        let rv = FileName::from_str(s);
+        assert!(rv.is_err());
+    }
+
+    ok_tester("GoodExecutable.exe");
+    err_tester("*.?xaml");
+    err_tester(r#"\\\lol///"#);
+}
+
+// endregion