diff --git a/src/library/entry.cr b/src/library/entry.cr
index dd50ed3..9fb1ef9 100644
--- a/src/library/entry.cr
+++ b/src/library/entry.cr
@@ -1,62 +1,27 @@
 require "image_size"
 require "yaml"
 
-class Entry
-  include YAML::Serializable
+abstract class Entry
+  getter id : String, book : Title, title : String,
+    size : String, pages : Int32, mtime : Time,
+    encoded_path : String, encoded_title : String, err_msg : String?
 
-  getter zip_path : String, book : Title, title : String,
-    size : String, pages : Int32, id : String, encoded_path : String,
-    encoded_title : String, mtime : Time, err_msg : String?
+  def initialize(
+    @id, @title, @book,
+    @size, @pages, @mtime,
+    @encoded_path, @encoded_title, @err_msg)
+  end
 
-  @[YAML::Field(ignore: true)]
-  @sort_title : String?
-
-  def initialize(@zip_path, @book)
-    storage = Storage.default
-    @encoded_path = URI.encode @zip_path
-    @title = File.basename @zip_path, File.extname @zip_path
-    @encoded_title = URI.encode @title
-    @size = (File.size @zip_path).humanize_bytes
-    id = storage.get_entry_id @zip_path, File.signature(@zip_path)
-    if id.nil?
-      id = random_str
-      storage.insert_entry_id({
-        path:      @zip_path,
-        id:        id,
-        signature: File.signature(@zip_path).to_s,
-      })
-    end
-    @id = id
-    @mtime = File.info(@zip_path).modification_time
-
-    unless File.readable? @zip_path
-      @err_msg = "File #{@zip_path} is not readable."
-      Logger.warn "#{@err_msg} Please make sure the " \
-                  "file permission is configured correctly."
-      return
-    end
-
-    archive_exception = validate_archive @zip_path
-    unless archive_exception.nil?
-      @err_msg = "Archive error: #{archive_exception}"
-      Logger.warn "Unable to extract archive #{@zip_path}. " \
-                  "Ignoring it. #{@err_msg}"
-      return
-    end
-
-    file = ArchiveFile.new @zip_path
-    @pages = file.entries.count do |e|
-      SUPPORTED_IMG_TYPES.includes? \
-        MIME.from_filename? e.filename
-    end
-    file.close
+  def self.new(ctx : YAML::ParseContext, node : YAML::Nodes::Node)
+    # TODO: check node? and select proper subclass
+    ZippedEntry.new ctx, node
   end
 
   def build_json(*, slim = false)
     JSON.build do |json|
       json.object do
-        {% for str in %w(zip_path title size id) %}
-        json.field {{str}}, @{{str.id}}
+        {% for str in %w(path title size id) %}
+        json.field {{str}}, {{str.id}}
       {% end %}
         if err_msg
           json.field "err_msg", err_msg
@@ -74,6 +39,9 @@ class Entry
     end
   end
 
+  @[YAML::Field(ignore: true)]
+  @sort_title : String?
+
   def sort_title
     sort_title_cached = @sort_title
     return sort_title_cached if sort_title_cached
@@ -131,58 +99,6 @@ class Entry
     url
   end
 
-  private def sorted_archive_entries
-    ArchiveFile.open @zip_path do |file|
-      entries = file.entries
-        .select { |e|
-          SUPPORTED_IMG_TYPES.includes? \
-            MIME.from_filename? e.filename
-        }
-        .sort! { |a, b|
-          compare_numerically a.filename, b.filename
-        }
-      yield file, entries
-    end
-  end
-
-  def read_page(page_num)
-    raise "Unreadble archive. #{@err_msg}" if @err_msg
-    img = nil
-    begin
-      sorted_archive_entries do |file, entries|
-        page = entries[page_num - 1]
-        data = file.read_entry page
-        if data
-          img = Image.new data, MIME.from_filename(page.filename),
-            page.filename, data.size
-        end
-      end
-    rescue e
-      Logger.warn "Unable to read page #{page_num} of #{@zip_path}. Error: #{e}"
-    end
-    img
-  end
-
-  def page_dimensions
-    sizes = [] of Hash(String, Int32)
-    sorted_archive_entries do |file, entries|
-      entries.each_with_index do |e, i|
-        begin
-          data = file.read_entry(e).not_nil!
-          size = ImageSize.get data
-          sizes << {
-            "width"  => size.width,
-            "height" => size.height,
-          }
-        rescue e
-          Logger.warn "Failed to read page #{i} of entry #{zip_path}. #{e}"
-          sizes << {"width" => 1000_i32, "height" => 1000_i32}
-        end
-      end
-    end
-    sizes
-  end
-
   def next_entry(username)
     entries = @book.sorted_entries username
     idx = entries.index self
@@ -197,20 +113,6 @@ class Entry
     entries[idx - 1]
   end
 
-  def date_added
-    date_added = nil
-    TitleInfo.new @book.dir do |info|
-      info_da = info.date_added[@title]?
-      if info_da.nil?
-        date_added = info.date_added[@title] = ctime @zip_path
-        info.save
-      else
-        date_added = info_da
-      end
-    end
-    date_added.not_nil! # is it ok to set not_nil! here?
-  end
-
   # For backward backward compatibility with v0.1.0, we save entry titles
   #   instead of IDs in info.json
   def save_progress(username, page)
@@ -290,7 +192,7 @@ class Entry
       end
       Storage.default.save_thumbnail @id, img
     rescue e
-      Logger.warn "Failed to generate thumbnail for file #{@zip_path}. #{e}"
+      Logger.warn "Failed to generate thumbnail for file #{path}. #{e}"
     end
 
     img
@@ -299,4 +201,139 @@ class Entry
   def get_thumbnail : Image?
     Storage.default.get_thumbnail @id
   end
+
+  def date_added : Time
+    date_added = nil
+    TitleInfo.new @book.dir do |info|
+      info_da = info.date_added[@title]?
+      if info_da.nil?
+        date_added = info.date_added[@title] = createtime
+        info.save
+      else
+        date_added = info_da
+      end
+    end
+    date_added.not_nil! # is it ok to set not_nil! here?
+  end
+
+  abstract def path : String
+
+  abstract def createtime : Time
+
+  abstract def read_page(page_num)
+
+  abstract def page_dimensions
+
+  abstract def exists? : Bool?
+end
+
+class ZippedEntry < Entry
+  include YAML::Serializable
+
+  getter zip_path : String
+
+  def initialize(@zip_path, @book)
+    storage = Storage.default
+    @encoded_path = URI.encode @zip_path
+    @title = File.basename @zip_path, File.extname @zip_path
+    @encoded_title = URI.encode @title
+    @size = (File.size @zip_path).humanize_bytes
+    id = storage.get_entry_id @zip_path, File.signature(@zip_path)
+    if id.nil?
+      id = random_str
+      storage.insert_entry_id({
+        path:      @zip_path,
+        id:        id,
+        signature: File.signature(@zip_path).to_s,
+      })
+    end
+    @id = id
+    @mtime = File.info(@zip_path).modification_time
+
+    unless File.readable? @zip_path
+      @err_msg = "File #{@zip_path} is not readable."
+      Logger.warn "#{@err_msg} Please make sure the " \
+                  "file permission is configured correctly."
+      return
+    end
+
+    archive_exception = validate_archive @zip_path
+    unless archive_exception.nil?
+      @err_msg = "Archive error: #{archive_exception}"
+      Logger.warn "Unable to extract archive #{@zip_path}. " \
+                  "Ignoring it. #{@err_msg}"
+      return
+    end
+
+    file = ArchiveFile.new @zip_path
+    @pages = file.entries.count do |e|
+      SUPPORTED_IMG_TYPES.includes? \
+        MIME.from_filename? e.filename
+    end
+    file.close
+  end
+
+  def path : String
+    @zip_path
+  end
+
+  def createtime : Time
+    ctime @zip_path
+  end
+
+  private def sorted_archive_entries
+    ArchiveFile.open @zip_path do |file|
+      entries = file.entries
+        .select { |e|
+          SUPPORTED_IMG_TYPES.includes? \
+            MIME.from_filename? e.filename
+        }
+        .sort! { |a, b|
+          compare_numerically a.filename, b.filename
+        }
+      yield file, entries
+    end
+  end
+
+  def read_page(page_num)
+    raise "Unreadble archive. #{@err_msg}" if @err_msg
+    img = nil
+    begin
+      sorted_archive_entries do |file, entries|
+        page = entries[page_num - 1]
+        data = file.read_entry page
+        if data
+          img = Image.new data, MIME.from_filename(page.filename),
+            page.filename, data.size
+        end
+      end
+    rescue e
+      Logger.warn "Unable to read page #{page_num} of #{@zip_path}. Error: #{e}"
+    end
+    img
+  end
+
+  def page_dimensions
+    sizes = [] of Hash(String, Int32)
+    sorted_archive_entries do |file, entries|
+      entries.each_with_index do |e, i|
+        begin
+          data = file.read_entry(e).not_nil!
+          size = ImageSize.get data
+          sizes << {
+            "width"  => size.width,
+            "height" => size.height,
+          }
+        rescue e
+          Logger.warn "Failed to read page #{i} of entry #{zip_path}. #{e}"
+          sizes << {"width" => 1000_i32, "height" => 1000_i32}
+        end
+      end
+    end
+    sizes
+  end
+
+  def exists? : Bool
+    File.exists? @zip_path
+  end
 end
diff --git a/src/library/title.cr b/src/library/title.cr
index e3d79d5..eeef8e7 100644
--- a/src/library/title.cr
+++ b/src/library/title.cr
@@ -55,7 +55,7 @@ class Title
         next
       end
       if is_supported_file path
-        entry = Entry.new path, self
+        entry = ZippedEntry.new path, self
         @entries << entry if entry.pages > 0 || entry.err_msg
       end
     end
@@ -127,12 +127,12 @@ class Title
 
     previous_entries_size = @entries.size
     @entries.select! do |entry|
-      existence = File.exists? entry.zip_path
+      existence = entry.exists?
       Fiber.yield
       context["deleted_entry_ids"] << entry.id unless existence
       existence
     end
-    remained_entry_zip_paths = @entries.map &.zip_path
+    remained_entry_zip_paths = @entries.map &.path
 
     is_titles_added = false
     is_entries_added = false
@@ -162,7 +162,7 @@ class Title
       end
       if is_supported_file path
         next if remained_entry_zip_paths.includes? path
-        entry = Entry.new path, self
+        entry = ZippedEntry.new path, self
         if entry.pages > 0 || entry.err_msg
           @entries << entry
           is_entries_added = true
@@ -627,7 +627,7 @@ class Title
 
     @entries.each do |e|
       next if da.has_key? e.title
-      da[e.title] = ctime e.zip_path
+      da[e.title] = ctime e.path
     end
 
     TitleInfo.new @dir do |info|
diff --git a/src/routes/api.cr b/src/routes/api.cr
index e664b28..03d6e53 100644
--- a/src/routes/api.cr
+++ b/src/routes/api.cr
@@ -40,7 +40,7 @@ struct APIRouter
     Koa.schema "entry", {
       "pages" => Int32,
       "mtime" => Int64,
-    }.merge(s %w(zip_path title size id title_id display_name cover_url)),
+    }.merge(s %w(path title size id title_id display_name cover_url)),
       desc: "An entry in a book"
 
     Koa.schema "title", {
@@ -1138,7 +1138,7 @@ struct APIRouter
         entry = title.get_entry eid
         raise "Entry ID `#{eid}` of `#{title.title}` not found" if entry.nil?
 
-        file_hash = Digest::SHA1.hexdigest (entry.zip_path + entry.mtime.to_s)
+        file_hash = Digest::SHA1.hexdigest (entry.path + entry.mtime.to_s)
         e_tag = "W/#{file_hash}"
         if e_tag == prev_e_tag
           env.response.status_code = 304
@@ -1172,7 +1172,7 @@ struct APIRouter
         title = (Library.default.get_title env.params.url["tid"]).not_nil!
         entry = (title.get_entry env.params.url["eid"]).not_nil!
 
-        send_attachment env, entry.zip_path
+        send_attachment env, entry.path
       rescue e
         Logger.error e
         env.response.status_code = 404
diff --git a/src/routes/reader.cr b/src/routes/reader.cr
index 40b86aa..052e212 100644
--- a/src/routes/reader.cr
+++ b/src/routes/reader.cr
@@ -53,6 +53,7 @@ struct ReaderRouter
         render "src/views/reader.html.ecr"
       rescue e
         Logger.error e
+        puts e.backtrace?
         env.response.status_code = 404
       end
     end
diff --git a/src/views/opds/title.xml.ecr b/src/views/opds/title.xml.ecr
index b159687..1d82490 100644
--- a/src/views/opds/title.xml.ecr
+++ b/src/views/opds/title.xml.ecr
@@ -29,7 +29,7 @@
         <link rel="http://opds-spec.org/image" href="<%= e.cover_url %>" />
         <link rel="http://opds-spec.org/image/thumbnail" href="<%= e.cover_url %>" />
 
-        <link rel="http://opds-spec.org/acquisition" href="<%= base_url %>api/download/<%= e.book.id %>/<%= e.id %>" title="Read" type="<%= MIME.from_filename e.zip_path %>" />
+        <link rel="http://opds-spec.org/acquisition" href="<%= base_url %>api/download/<%= e.book.id %>/<%= e.id %>" title="Read" type="<%= MIME.from_filename e.path %>" />
 
         <link type="text/html" rel="alternate" title="Read in Mango" href="<%= base_url %>reader/<%= e.book.id %>/<%= e.id %>" />
         <link type="text/html" rel="alternate" title="Open in Mango" href="<%= base_url %>book/<%= e.book.id %>" />
diff --git a/src/views/reader-error.html.ecr b/src/views/reader-error.html.ecr
index 62a80fc..ad3580f 100644
--- a/src/views/reader-error.html.ecr
+++ b/src/views/reader-error.html.ecr
@@ -5,7 +5,7 @@
       <div>
         <h3 class="uk-modal-title uk-margin-remove-top">Error</h3>
       </div>
-      <p class="uk-text-meta uk-margin-remove-bottom"><%= entry.zip_path %></p>
+      <p class="uk-text-meta uk-margin-remove-bottom"><%= entry.path %></p>
       <p class="uk-text-meta uk-margin-remove-top"><%= entry.err_msg %></p>
     </div>
     <div class="uk-modal-body">
diff --git a/src/views/reader.html.ecr b/src/views/reader.html.ecr
index feac115..19e2b19 100644
--- a/src/views/reader.html.ecr
+++ b/src/views/reader.html.ecr
@@ -67,7 +67,7 @@
         <button class="uk-modal-close-default" type="button" uk-close></button>
         <div class="uk-modal-header">
           <h3 class="uk-modal-title break-word"><%= entry.display_name %></h3>
-          <p class="uk-text-meta uk-margin-remove-bottom break-word"><%= entry.zip_path %></p>
+          <p class="uk-text-meta uk-margin-remove-bottom break-word"><%= entry.path %></p>
         </div>
         <div class="uk-modal-body">
           <div class="uk-margin">